Recursos de colección

Caltech Authors (157.532 recursos)

Repository of works by Caltech published authors.

Status = In Press

Mostrando recursos 1 - 20 de 993

  1. Canyon effect and seasonal variability of deep-sea organisms in the NW Mediterranean: synchronous, year-long captures of "swimmers" from near-bottom sediment traps in a submarine canyon and its adjacent open slope

    Romano, C.; Flexas, M. M.; Segura, M.; Román, S.; Bahamon, N.; Gili, J. M.; Sanchez-Vidal, A.; Martin, D.
    Numerous organisms, including both passive sinkers and active migrators, are captured in sediment traps together with sediments. By capturing these “swimmers”, the traps become an extraordinarily tool to obtain relevant information on the biodiversity and dynamics of deep-sea organisms. Here we analyze near-bottom swimmers larger than 500 μm and their fluxes collected from eight near-bottom sediment traps installed on instrumented moorings deployed nearby Blanes Canyon (BC). Our data, obtained from November 2008 to October 2009 with a sampling rate of 15 days, constitutes the first year-long, continuous time series of the whole swimmers’ community collected at different traps and bottom...

  2. Real-Time In Vivo Intraocular Pressure Monitoring using an Optomechanical Implant and an Artificial Neural Network

    Kim, Kun ho; Lee, Jeong Oen; Du, Juan; Sretavan, David; Choo, Hyuck
    Optimized glaucoma therapy requires frequent monitoring and timely lowering of elevated intraocular pressure (IOP). A recently developed microscale IOP-monitoring implant, when illuminated with broadband light, reflects a pressure-dependent optical spectrum that is captured and converted to measure IOP. However, its accuracy is limited by background noise and the difficulty of modeling non-linear shifts of the spectra with respect to pressure changes. Using an end-to-end calibration system to train an artificial neural network (ANN) for signal demodulation we improved the speed and accuracy of pressure measurements obtained with an optically probed IOP-monitoring implant and make it suitable for real-time in vivo...

  3. A Thermodynamic Investigation of Adsorbate-Adsorbate Interactions of Carbon Dioxide on Nanostructured Carbons

    Murialdo, Maxwell; Ahn, Channing C.; Fultz, Brent
    A thermodynamic study of carbon dioxide adsorption on a zeolite-templated carbon (ZTC), a superactivated carbon (MSC-30) and an activated carbon (CNS-201) was carried out at temperatures from 241 to 478 K and pressures up to 5.5•10^6 Pa. Excess adsorption isotherms were fitted with generalized Langmuir-type equations, allowing the isosteric heats of adsorption and adsorbed-phase heat capacities to be obtained as a function of absolute adsorption. On MSC-30, a superactivated carbon, the isosteric heat of carbon dioxide adsorption increases with occupancy from 19 to 21 kJ•mol^(−1), before decreasing at high loading. This increase is attributed to attractive adsorbate-adsorbate intermolecular interactions as...

  4. A generalized electro-elastic theory of polymer networks

    Cohen, Noy
    A rigorous multi-scale analysis of the electromechanical coupling in dielectric polymers is conducted. The body couples stemming from a misalignment between the electric field and the electric-dipole density vector are studied and the conservation laws for polymer networks are derived. Using variational principles, expressions for the polarization and the stress are determined. Interestingly, it is found that the stress tensor resulting from coupled loadings in which the electric field is misaligned with the principal stretch directions is not symmetric and the asymmetry arises from the body couples. Next, the electro-mechanical response of a chain is analyzed. The deformations of the...

  5. The Oxygen Reduction Reaction on Graphene from Quantum Mechanics: Comparing Armchair and Zigzag Carbon Edges

    Ly, Quang; Merinov, Boris V.; Xiao, Hai; Goddard, William A., III; Yu, Ted
    Using density functional theory (PBE-D2 flavor), we report the mechanism for the oxygen reduction reaction (ORR) on graphene sheets. We find that ORR starts with OO chemisorbing onto the carbon edges, rather than the basal plane face, which is not energetically favorable. The carbon edges were described as one-dimensional periodic graphene ribbons with both armchair and zigzag edges. We calculated the binding energies of the ORR products (OO, OOH, O, OH, HOH, HOOH) for the zigzag and armchair edges, examining both the Langmuir Hinshelwood (LH) and Eley-Rideal (ER), to understand how OO is reduced. For the armchair edge, we calculate...

  6. Nitrogen Fixation via a Terminal Fe(IV) Nitride

    Thompson, Niklas B.; Green, Michael T.; Peters, Jonas C.
    Terminal iron nitrides (Fe≡N) have been proposed as intermediates of (bio)catalytic nitrogen fixation, yet experimental evidence to support this hypothesis has been lacking. In particular, no prior synthetic examples of terminal Fe≡N species have been derived from N_2. Here we show that a nitrogen-fixing Fe-N_2 catalyst can be protonated to form an Fe(NNH_2) hydrazido(2−) intermediate, which, upon further protonation, heterolytically cleaves the N–N bond to release [Fe^(IV)≡N]^+ and NH_3. These observations provide direct evidence for the viability of a Chatt-type (distal) mechanism for Fe-mediated N_2-to-NH_3 conversion. The physical oxidation state range of the Fe complexes in this transformation is buffered...

  7. Terminal Molybdenum Phosphides with d Electrons: Radical Character Promotes Coupling Chemistry

    Buss, Joshua A.; Oyala, Paul H.; Agapie, Theodor
    A terminal Mo phosphide was prepared through the group transfer of both P and Cl atoms from chloro-substituted dibenzo-7λ^3-phosphanorbornadiene. This compound represents the first structurally characterized terminal transition-metal phosphide with valence d electrons. In the tetragonal ligand field, these electrons populate an orbital of d_(xy) parentage, an electronic configuration that accommodates both metal d electrons and a formal M≡P triple bond. Single-electron oxidation affords a transient open-shell terminal phosphide cation with significant spin density on P, as corroborated by continuous wave (CW) and pulse electron paramagnetic resonance (EPR) characterization. Facile P−P bond formation occurs from this species through intermolecular phosphide...

  8. Synthesis and Evaluation of Sterically Demanding Ruthenium Dithiolate Catalysts for Stereoretentive Olefin Metathesis

    Montgomery, T. Patrick; Grandner, Jessica M.; Houk, K. N.; Grubbs, Robert H.
    Dithiolate ligands have recently been used in ruthenium-catalyzed olefin metathesis and have provided access to a kinetically E selective pathway through stereoretentive olefin metathesis. The typical dithiolate used is relatively simple with low steric demands imparted on the catalyst. We have developed a synthetic route that allows access to sterically demanding dithiolate ligands. The catalysts generated provided a pathway to study the intricate structure–activity relationships in olefin metathesis. It was found that DFT calculations can predict the ligand arrangement around the ruthenium center with remarkable accuracy. These dithiolate catalysts proved resistant to ligand isomerization and were stable even under forcing...

  9. Weakening of the North American monsoon with global warming

    Salvatore, Pascal; Boos, William R.; Bordoni, Simona; Delworth, Thomas L.; Kapnick, Sarah B.; Murakami, Hiroshi; Vecchi, Gabriel A.; Zhang, Wei
    Future changes in the North American monsoon, a circulation system that brings abundant summer rains to vast areas of the North American Southwest, could have significant consequences for regional water resources. How this monsoon will change with increasing greenhouse gases, however, remains unclear, not least because coarse horizontal resolution and systematic sea-surface temperature biases limit the reliability of its numerical model simulations. Here we investigate the monsoon response to increased atmospheric carbon dioxide (CO_2) concentrations using a 50-km-resolution global climate model which features a realistic representation of the monsoon climatology and its synoptic-scale variability. It is found that the monsoon...

  10. Genetic separation of Sae2 nuclease activity from Mre11 nuclease functions in budding yeast

    Arora, Sucheta; Deshpande, Rajashree A.; Budd, Martin; Campbell, Judy; Revere, America; Zhang, Xiaoming; Schmidt, Kristina H.; Paull, Tanya T.
    Sae2 promotes the repair of DNA double-strand breaks in Saccharomyces cerevisiae. The role of Sae2 is linked to the Mre11/Rad50/Xrs2 (MRX) complex, which is important for the processing of DNA ends into single-stranded substrates for homologous recombination. Sae2 has intrinsic endonuclease activity, but the role of this activity has not been assessed independently from its functions in promoting Mre11 nuclease activity. Here we identify and characterize separation-of-function mutants that lack intrinsic nuclease activity or the ability to promote Mre11 endonucleolytic activity. We find that the ability of Sae2 to promote MRX nuclease functions is important for DNA damage survival, particularly in...

  11. IKKβ and mutant huntingtin interactions regulate the expression of IL-34: implications for microglial-mediated neurodegeneration in HD

    Khoshnan, Ali; Sabbaugh, Adam; Calamini, Barbara; Marinero, Steven A.; Dunn, Denise E.; Yoo, Jung Hyun; Ko, Jan; Lo, Donald C.; Patterson, Paul H.
    Neuronal interleukin-34 (IL-34) promotes the expansion of microglia in the central nervous system—microglial activation and expansion are in turn implicated in the pathogenesis of Huntington‘s disease (HD). We thus examined whether the accumulation of an amyloidogenic exon-1 fragment of mutant huntingtin (mHTTx1) modulates the expression of IL-34 in dopaminergic neurons derived from a human embryonic stem cell line. We found that mHTTx1 aggregates induce IL-34 production selectively in post-mitotic neurons. Exposure of neurons to DNA damaging agents or the excitotoxin NMDA elicited similar results suggesting that IL-34 induction may be a general response to neuronal stress including the accumulation of...

  12. Ultrahigh Mass Activity for Carbon Dioxide Reduction Enabled by Gold-iron Core-shell Nanoparticles

    Sun, Kun; Cheng, Tao; Wu, Lina; Hu, Yongfeng; Zhou, Jigang; MacLennan, Aimee; Jiang, Zhaohua; Gao, Yunzhi; Goddard, William A., III; Wang, Zhijiang
    Wide application of carbon dioxide (CO_2) electrochemical energy storage requires catalysts with high mass activity. Alloy catalysts can achieve superior performance to single metals while reducing the cost by finely-tuning the composition and morphology. We used in silico Quantum Mechanics Rapid Screening to identify Au-Fe as a candidate improving CO_2 reduction, and then synthesized and tested it experimentally. The synthesized Au-Fe alloy catalyst evolves quickly into a stable Au-Fe core-shell nanoparticle (AuFe-CSNP) after leaching out surface Fe. This AuFe-CSNP exhibits exclusive CO selectivity, long-term stability, nearly a hundred-fold increase in mass activity towards CO_2 reduction compared with Au NP, and...

  13. Gaze-stabilizing central vestibular neurons project asymmetrically to extraocular motoneuron pools

    Schoppik, David; Bianco, Isaac H.; Prober, David A.; Douglass, Adam D.; Robson, Drew N.; Li, Jennifer M. B.; Greenwood, Joel S. F.; Soucy, Edward; Engert, Florian; Schier, Alexander F.
    Within reflex circuits, specific anatomical projections allow central neurons to relay sensations to effectors that generate movements. A major challenge is to relate anatomical features of central neural populations —- such as asymmetric connectivity —- to the computations the populations perform. To address this problem, we mapped the anatomy, modeled the function, and discovered a new behavioral role for a genetically-defined population of central vestibular neurons in rhombomeres 5-7 of larval zebrafish. First, we found that neurons within this central population project preferentially to motoneurons that move the eyes downward. Concordantly, when the entire population of asymmetrically-projecting neurons was stimulated...

  14. PyLasso: a PyMOL plugin to identify lassos

    Gierut, Aleksandra M.; Niemyska, Wanda; Dabrowski-Tumanski, Pawel; Sułkowski, Piotr; Sulkowska, Joanna I.
    Entanglement in macromolecules is an important phenomenon and a subject of multidisciplinary research. As recently discovered, around 4% of proteins form new entangled motifs, called lassos. Here we present the PyLasso—a PyMOL plugin to identify and analyse properties of lassos in proteins and other (bio)polymers, as well as in other biological, physical and mathematical systems. The PyLasso is a useful tool for all researchers working on modeling of macromolecules, structure prediction, properties of polymers, entanglement in fluids and fields, etc.

  15. High capacity V-based metal hydride electrodes for rechargeable batteries

    Yang, Heng; Weadock, Nicholas J.; Tan, Hongjin; Fultz, Brent
    We report the successful development of Ti_(29)V_(62−x)Ni_9Cr_x (x = 0, 6, 12) body centered cubic metal hydride (MH) electrodes by addressing vanadium corrosion and dissolution in KOH solutions. By identifying oxygen as the primary source of corrosion and eliminating oxygen with an Ar-purged cell, the Cr-free Ti_(29)V_(62)Ni_9 alloy electrode achieved a maximum capacity of 594 mAh g^(-1), double the capacity of commercial AB_5 MH electrodes. With coin cells designed to minimize oxygen evolution, the cycle stability of a Ti_(29)V_(62)Ni_9 alloy electrode was greatly improved with either vanadate ion additions to the electrolyte or Cr-substitution in the alloy. Together, both approaches...

  16. Unified Distributed Control of Stand-alone DC Microgrids

    Wang, Zhaojian; Liu, Feng; Chen, Ying; Low, Steven H.; Mei, Shengwei
    Stand-alone direct current (DC) microgrids may belong to different owners and adopt various control strategies. This brings great challenge to its optimal operation due to the difficulty of implementing a unified control. This paper addresses the distributed optimal control of DC microgrids, which intends to break the restriction of diversity to some extent. Firstly, we formulate the optimal power flow (OPF) problem of stand-alone DC microgrids as an exact second order cone program (SOCP) and prove the uniqueness of the optimal solution. Then a dynamic solving algorithm based on primal-dual decomposition method is proposed, the convergence of which is proved...

  17. Position-specific ^(13)C distributions within propane from experiments and natural gas samples

    Piasecki, Alison; Sessions, Alex; Lawson, Michael; Ferreira, A. A.; Santos Neto, E. V.; Ellis, Geoffrey S.; Lewan, Michael D.; Eiler, John M.
    Site-specific carbon isotope measurements of organic compounds potentially recover information that is lost in a conventional, ‘bulk' isotopic analysis. Such measurements are useful because isotopically fractionating processes may have distinct effects at different molecular sites, and thermodynamically equilibrated populations of molecules tend to concentrate heavy isotopes in one molecular site versus another. Most recent studies of site-specific ^(13)C in organics use specialized Nuclear Magnetic Resonance (NMR) techniques or complex chemical degradations prior to mass spectrometric measurements. Herein we present the first application of a new mass spectrometric technique that reconstructs the site-specific carbon isotope composition of propane based on measurements...

  18. Stress- and Structure-Induced Anisotropy in Southern California From Two Decades of Shear Wave Splitting Measurements

    Li, Zefeng; Peng, Zhigang
    We measure shear wave splitting (SWS) parameters (i.e., fast direction and delay time) using 330,000 local earthquakes recorded by more than 400 stations of the Southern California Seismic Network (1995–2014). The resulting 232,000 SWS measurements (90,000 high-quality ones) provide a uniform and comprehensive database of local SWS measurements in Southern California. The fast directions at many stations are consistent with regional maximum compressional stress σ_(Hmax). However, several regions show clear deviations from the σ_(Hmax) directions. These include linear sections along the San Andreas Fault and the Santa Ynez Fault, geological blocks NW to the Los Angeles Basin, regions around the...

  19. Special issue on global flow instability and control

    Sharma, Ati; Theofilis, Vassilis; Colonius, Tim
    This special issue is the second on the topic of “Global Flow Instability and Control,” following the first in 2011. As with the previous special issue, the participants of the last two symposia on Global Flow Instability and Control, held in Crete, Greece, were invited to submit publications. These papers were peer reviewed according to the standards of the journal, and this issue represents a snapshot of the progress since 2011. In this preface, a sampling of important developments in the field since the first issue is discussed. A synopsis of the papers in this issue is given in that...

  20. Methyl-compound use and slow growth characterize microbial life in 2-km-deep subseafloor coal and shale beds

    Trembath-Reichert, Elizabeth; Morono, Yuki; Ijiri, Akira; Hoshino, Tatsuhiko; Dawson, Katherine S.; Inagaki, Fumio; Orphan, Victoria J.
    The past decade of scientific ocean drilling has revealed seemingly ubiquitous, slow-growing microbial life within a range of deep biosphere habitats. Integrated Ocean Drilling Program Expedition 337 expanded these studies by successfully coring Miocene-aged coal beds 2 km below the seafloor hypothesized to be “hot spots” for microbial life. To characterize the activity of coal-associated microorganisms from this site, a series of stable isotope probing (SIP) experiments were conducted using intact pieces of coal and overlying shale incubated at in situ temperatures (45 °C). The 30-month SIP incubations were amended with deuterated water as a passive tracer for growth and...

Aviso de cookies: Usamos cookies propias y de terceros para mejorar nuestros servicios, para análisis estadístico y para mostrarle publicidad. Si continua navegando consideramos que acepta su uso en los términos establecidos en la Política de cookies.