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Caltech Authors (132.208 recursos)

Repository of works by Caltech published authors.

Type = Conference or Workshop Item

Mostrando recursos 1 - 20 de 654

  1. High Order Super Nested Arrays

    Liu, Chun-Lin; Vaidyanathan, P. P.
    Mutual coupling between sensors has a negative impact on the estimation of directions of arrival (DOAs). Sparse arrays such as nested arrays, coprime arrays, and minimum redundancy arrays (MRAs) have less mutual coupling than uniform linear arrays (ULAs). These sparse arrays also have a difference coarray of size O(N^2), where N is the number of sensors, and can therefore resolve O(N^2) uncorrelated source directions. The various sparse arrays proposed in the literature have their pros and cons. The nested array is practical and easy to use but has a dense ULA part which suffers from mutual coupling effects like the...

  2. Acceleration-driven variable-density turbulent flow

    Gat, Ilana; Matheou, Georgios; Chung, Daniel; Dimotakis, Paul E.
    We discuss turbulent dynamics and mixing of a variable-density flow subject to a uniform-acceleration field. The flow and misalignments of pressure and density gradients are investigated for small to large density ratios, with evidence that the small-density ratio flow is described by the Boussinesq approximation. A new shear-layer growth rate is reported, along with an extension of uniform-density flow vorticity-alignment statistics in the variable-density ow studied. Spectra collapse when properly scaled for variable density.

  3. Conformation of the backbone of bottlebrush polymers

    Kim, Joey; Kornfield, Julia
    Bottlebrush polymers are a hierarchal arrangement of linear polymer chains into two domains: the side chain domain (which disfavors crowding) densely grafted onto a backbone domain (which resists stretching). The net result of the interactions between the two domains is a relatively expanded conformation of the backbone. Despite numerous theor., simulation and exptl. approaches, there is still controversy on the soln. behavior of bottlebrush polymers. Exptl., a main problem can be attributed to limitations that result from the complex architecture; isolating the behavior of each domain is very difficult. Therefore, exptl. detn. on each domain thus far has only been inferred from the overall structure...

  4. Detection of Organic-Rich Oil Shales of the Green River Formation, Utah, with Ground-Based Imaging Spectroscopy

    Greenberger, Rebecca N.; Ehlmann, Bethany L.; Jewell, Paul W.; Birgenheier, Lauren P.; Green, Robert O.
    Oil shales contain abundant immature organic matter and are a potential unconventional petroleum resource. Prior studies have used visible/shortwave infrared imaging spectroscopy to map surface exposures of deposits from satellite and airborne platforms and image cores in the laboratory. Here, we work at an intermediate, outcrop-scale, testing the ability of field-based imaging spectroscopy to identify oil shale strata and characterize the depositional environments that led to enrichment of organic matter in sedimentary rocks within the Green River Formation, Utah, USA. The oil shale layers as well as carbonates, phyllosilicates, gypsum, hydrated silica, and ferric oxides are identified in discrete lithologic...

  5. Using VSWIR Microimaging Spectroscopy to Explore the Mineralogical Diversity of HED Meteorites

    Fraeman, Abigail A.; Ehlmann, Bethany L.; Northwood-Smith, Geraint W. D.; Liu, Yang; Wadhwa, Meenakshi; Greenberger, Rebecca N.
    We use VSWIR microimaging spectroscopy to survey the spectral diversity of HED meteorites at 80-μm/pixel spatial scale. Our goal in this work is both to explore the emerging capabilities of microimaging VSWIR spectroscopy and to contribute to understanding the petrologic diversity of the HED suite and the evolution of Vesta. Using a combination of manual and automated hyperspectral classification techniques, we identify four major classes of materials based on VSWIR absorptions that include pyroxene, olivine, Fe-bearing feldspars, and glass-bearing/featureless materials. Results show microimaging spectroscopy is an effective method for rapidly and non-destructively characterizing small compositional variations of meteorite samples and...

  6. Identifying and Quantifying Mineral Abundance through VSWIR Microimaging Spectroscopy: A Comparison to XRD and SEM

    Leask, Ellen K.; Ehlmann, Bethany L.
    Visible-shortwave infrared microimaging reflectance spectroscopy is a new technique to identify minerals, quantify abundances, and assess textural relationships at sub-millimetre scale without destructive sample preparation. Here we used a prototype instrument to image serpentinized igneous rocks and carbonate-rich travertine deposits to evaluate performance, relative to traditional techniques: XRD (mineralogical analysis of bulk powders with no texture preservation) and SEM/EDS (analysis of phases and textures using chemical data from polished thin sections). VSWIR microimaging spectroscopy is ideal for identifying spatially coherent rare phases, below XRD detection limits. The progress of alteration can also be inferred from spectral parameters and may correspond...

  7. Rare Jarosite Detection in CRISM Imagery by Non-Parametric Bayesian Clustering

    Dundar, Murat; Ehlmann, Bethany L.
    Discovery of rare phases on Mars is important as they serve as indicators of the geochemistry of the Mars surface and facilitate understanding of mineral assemblages within a geologic unit. Identification of rare minerals in high spatial and spectral resolution Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) visible/shortwave infrared (VSWIR) images has been a challenge due to the presence of both additive and multiplicative noise and other artifacts, affecting all collected images, in addition to the limited spatial extent of regions hosting these minerals. In an effort to automate this task we evaluate various clustering algorithms using the detection of rare jarosite, associated with spectrally similar minerals in CRISM imagery, as a...

  8. Cascading compliance requirements for thesis-related data and software: A survey of institutional policy at American (AAU) research universities

    Clement, Gail P.
    According to the CODATA/Research Data Alliance Principles on the Legal Interoperability of Research Data (https://rd-alliance.org/group/rdacodata-legal-interoperability-ig/wiki/legal-principles-data.html), the distribution and dissemination of research data (including software) is, to a significant extent, governed by law and institutional policy that specify ownership of these research outputs and the rights such ownership conveys. In the United States, copyright does not affix to purely factual information, but may govern sharing and reuse of protectable elements in a dataset (selection, arrangement, database design, and documentation) and software (original code, comments, and documentation). Moreover, institutional policy may establish that ownership of research data and software belongs to the...

  9. Synthetic probes for understanding glycosaminoglycan recognition and signaling in the brain

    Hsieh-Wilson, Linda C.
    Glycosaminoglycans (GAGs) comprise a large family of sulfated polysaccharides that regulate diverse biol. events such as embryonic development, viral invasion, cancer metastasis, and spinal cord injury. Assembled from repeating disaccharide subunits, GAGs exhibit subtle variations in stereochem., chain length, and patterns of sulfation. This structural diversity is thought to enable the generation of a large no. of protein-binding motifs. We will describe the synergistic application of org. chem. and neurobiol. to understand how specific GAG structures interact with protein receptors in the brain. In addn., we will discuss recent work on GAG-based polymer mimetics, which have enabled the first explorations...

  10. Molecular Marker Analysis as a Guide to the Sources of Fine Organic Aerosols

    Rogge, W. F.; Cass, G. R.; Hildemann, L. M.; Mazurek, M. A.; Simoneit, B. R. T.
    The molecular composition of fine particulate (D_p ≥ 2 µm) organic aerosol emissions from the most important sources in the Los Angeles area has been determined. Likewise, ambient concentration patterns for more than 80 single organic compounds have been measured at four urban sites (West Los Angeles, Downtown Los Angeles, Pasadena, and Rubidoux) and at one remote offshore site (San Nicolas Island). It has been found that cholesterol serves as a marker compound for emissions from charbroilers and other meat cooking operations. Vehicular exhaust being emitted from diesel and gasoline powered engines can be traced in the Los Angeles atmosphere...

  11. Development of solar fuels photoanodes through combinatorial integration of Ni-La-Co-Ce oxide and Ni-Fe-Co-Ce oxide catalysts on BiVO_4

    Haber, Joel; Guevarra, Dan; Shinde, Aniketa; Zhou, Lan; Liu, Guiji; Sharp, Ian; Toma, Francesca; Gregoire, John
    The development of an efficient, stable photoanode to provide protons and electrons to the (photo)cathode remains a primary materials challenge in the establishment of a scalable technol. for solar fuels generation. The typical photoanode architecture consists of a semiconductor light absorber coated with a metal oxide that serves a combination of functions, including corrosion protection, electrocatalysis, light trapping, hole transport, and elimination of deleterious recombination sites. To provide a more efficient exploration of metal oxide coatings for a given light absorber, we introduce a high throughput methodol. wherein a uniform BiVO_4 library is coated with 858 unique metal oxides covering...

  12. Roving Reference: Getting out in the Wild

    Painter, Joy A.
    [no abstract]

  13. Droplet Breakup in High-Speed Gas Flows

    Meng, Jomela C.; Colonius, Tim
    Numerical simulations are performed to study the breakup of water cylinders in the flow behind normal shocks. The computational setup is similar to previous experiments (Igra and Takayama, 2001, 2003). We examine the qualitative features of the so-called stripping breakup observed in the numerical results. Two interesting flow features are discussed: the existence of recirculation regions and an upstream jet in the wake. Various integral quantities associated with the cylinder’s deformation and acceleration are computed and compared with the experimental results, with generally good agreement. Furthermore, calculations of the velocity and acceleration of the cylinder’s center of mass provide an...

  14. Using the Research of Others Responsibly: An Overview of Attribution, Copyright, and Authorship Ethics

    Clement, Gail P.; Wrublewski, Donna
    [no abstrac]

  15. Natural and non-canonical mutagenesis studies of receptor gating in 5-HT3A receptors

    Mosesso, Richard; Lummis, Sarah C. R.; Dougherty, Dennis A.
    The 5-HT_(3A) receptor is a homopentameric ligand-gated ion channel belonging to the Cys-loop family of receptors, members of which have many functions and are important targets for a variety of diseases. Previously, our lab has elucidated key binding interactions between these receptors and their ligands. However, the "gating" events that link binding of ligand to receptor activation are less well characterized. While obtaining high-resoln. crystal structures of transmembrane proteins can be difficult, a recent crystal structure of the mouse 5-HT_(3A) receptor has guided our search for intramol. interactions involved in gating. Focusing on regions identified to be important for gating in homologous receptors, we have...

  16. Evidence for in situ catalyst modification in atom transfer radical reactions with ruthenium benzylidene complexes

    Lee, Juneyoung; Grandner, Jessica M.; Engle, Keary; Houk, Kendall N.; Grubbs, Robert H.
    Since the first report of ruthenium- based catalysts in atom transfer radical addn. (ATRA, also called Kharasch addn.) and atom transfer radical polymn. (ATRP) , this area of research has attracted widespread interest. Well- defined ruthenium benzylidene complexes, commonly used as olefin metathesis catalysts, have also been reported to catalyze ATRA and ATRP. The ability of ruthenium benzylidene complexes to promote two reactions with such markedly different mechanisms has been utilized in various tandem reactions in which olefin metathesis and atom transfer radical (ATR) reactions take place in one pot. While the mechanism by which ruthenium benzylidenes initiate and catalyze olefin metathesis has been studied...

  17. Mechanistic investigation of proton reduction by cobaloximes: Insight from H2 oxidation kinetics

    Del Ciello, Sarah A.; Winkler, Jay R.; Peters, Jonas C.; Gray, Harry B.
    Cobaloximes are a class of earth- abundant proton redn. catalysts that have been known since the 1980's. Previous studies have come to conflicting conclusions about the mechanism of proton redn. by these catalysts, with evidence existing for both a homolytic and heterolytic mechanism. In this work, kinetic anal. of the reverse reaction is used to gain further insight.

  18. Cation-π interactions: Computational analyses of the aromatic box motif and the fluorination strategy for experimental evaluation of cys-loop receptors and related structures

    Davis, Matthew R.; Dougherty, Dennis A.
    Cation-π interactions are common in biol. systems, in particular ligand- gated ion channels (LGICs). Our own studies, in addn. to more recent structural studies, have revealed the arom. box as a common motif for binding cationic ligands. With the aim of understanding the nature of the arom. box, several computational methods were evaluated for their ability to reproduce exptl. cation-π binding energies. We find the DFT method M06 with the 6-31G(d, p) basis set performs best of several methods tested. The binding of benzene to a no. of different cations (sodium, potassium, ammonium, tetramethylammonium, and guanidinium) was studied. In addn., the binding of the org....

  19. Chemically specific dynamic bond percolation model for computational screening of polymer electrolytes

    Webb, Michael; Savoie, Brett; Wang, Zhen-Gang; Miller, Thomas
    Polymer electrolytes have significant promise for many lithium-ion battery applications because they are non-flammable, electrochem. stable, and easily manufd. However, significant improvements in the ionic cond. of even state- of-the-art polymer electrolytes is needed for technol. viability. The computationally- guided design of more conductive polymer electrolytes would save significant time and monetary resources, but these efforts require both a better understanding of ion- transport mechanisms in polymers and the development of tools for screening candidate polymers prior to synthesis and characterization. Using atomistic mol. dynamics (MD) simulations, we provide new insights into the mechanisms of lithium-ion diffusion in polymer electrolyte materials, including that the spatial distribution...

  20. Reduction of CO2 on Cu and Au/W electrode surfaces: A study by differential electrochemical mass spectrometry

    Javier, Alnald; Baricuatro, Jack; Kim, Youn-Geun; Soriaga, Manuel
    This work describes results from an attempt to employ differential electrochem. mass spectrometry (DEMS) of selectively pre-adsorbed reactants and (postulated) intermediates as a supplementary exptl. approach in the study of the reaction mechanism of the Cu-catalyzed electrochem. redn. of CO2. The results prompt the following empirical inferences: (i) CO is the first product of CO2 redn., as well as the first intermediate in more advanced reactions that include formation of pure and oxygenated hydrocarbons; this is in conformity with the (almost) unanimously held view. (ii) HCHO is not a precursor for C=C double-bond formation. (iii) HCHO is an intermediate for the prodn. of methane...

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