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Caltech Authors (147.820 recursos)

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Mostrando recursos 1 - 20 de 54.970

  1. Measuring Flux Distributions for Diffusion in the Small-Numbers Limit

    Seitaridou, Effrosyni; Inamdar, Mandar M.; Phillips, Rob; Ghosh, Kingshuk; Dill, Ken
    For the classical diffusion of independent particles, Fick's law gives a well-known relationship between the average flux and the average concentration gradient. What has not yet been explored experimentally, however, is the dynamical distribution of diffusion rates in the limit of small particle numbers. Here, we measure the distribution of diffusional fluxes using a microfluidics device filled with a colloidal suspension of a small number of microspheres. Our experiments show that (1) the flux distribution is accurately described by a Gaussian function; (2) Fick's law, that the average flux is proportional to the particle gradient, holds even for particle gradients...

  2. Mechanistic Investigation of β-Galactosidase-Activated MR Contrast Agents

    Urbanczyk-Pearson, Lauren M.; Femia, Frank J.; Smith, Jeffrey; Parigi, Giacomo; Duimstra, Joseph A.; Eckermann, Amanda L.; Luchinat, Claudio; Meade, Thomas J.
    We report a mechanistic investigation of an isomeric series of β-galactosidase-activated magnetic resonance contrast agents. Our strategy focuses on the synthesis of macrocyclic caged-complexes that coordinatively saturate a chelated lanthanide. Enzyme cleavage of the complex results in an open coordination site available for water that creates a detectable MR contrast agent. The complexes consist of a DO3A Gd(III) chelator modified with a galactopyranose at the N-10 position of the macrocycle. We observed significant differences in relaxometric properties and coordination geometry that can be correlated to subtle variations of the linker between the macrocycle and the galactopyranose. After synthesis and purification...

  3. Elastic-plastic bending of the lithosphere incorporating rock deformation data, with application to the structure of the Hawaiian archipelago

    Hsi-Ping, Liu; Kosloff, Dan
    An elastic-plastic lithosphere bending model incorporating rock deformation data has been developed for computation of flexure profiles at mid-ocean island chains and at the trenches near the plate boundaries. Flexure of the plate is computed by finite-element numerical solution of Von Kármán's equation for large deflection of plates with a nonlinear material behavior. The elastic part of the constitutive relation is derived from seismology (moduli = 90% of the seismic values) while the strain rate-dependent plastic part is derived from dunite deformation data extrapolated to the appropriate geologic loading rates. As an illustration, the amplitude and the wavelength of the...

  4. Outstanding hydrogen evolution reaction catalyzed by porous nickel diselenide electrocatalysts

    Zhou, Haiqing; Yu, Fang; Liu, Yuanyue; Sun, Jingying; Zhu, Zhuan; He, Ran; Bao, Jiming; Goddard, William A., III; Chen, Shuo; Ren, Zhifeng
    To relieve our strong reliance on fossil fuels and to reduce greenhouse effects, there is an ever-growing interest in using electrocatalytic water splitting to produce green, renewable, and environment-benign hydrogen fuel via the hydrogen evolution reaction. For commercially feasible water electrolysis, it is imperative to develop electrocatalysts that perform as efficiently as Pt but using only earth-abundant commercial materials. However, the highest performance current catalysts consist of nanostructures made by using complex methods. Here we report a porous nickel diselenide (NiSe_2) catalyst that is superior for water electrolysis, exhibiting much better catalytic performance than most first-row transition metal dichalcogenide-based catalysts,...

  5. A note on low energy scattering for homogeneous long range potentials

    Frank, Rupert L.
    We explicitly calculate the scattering matrix at energy zero for attractive, radial and homogeneous long-range potentials. This proves a conjecture by Derezinski and Skibsted.

  6. Pulsed laser-deposited n-Si/NiO_x photoanodes for stable and efficient photoelectrochemical water splitting

    He, Lingyun; Zhou, Wu; Cai, Dongping; Mao, Samuel S.; Sun, Ke; Shen, Shaohua
    An electrocatalytic and stable nickel oxide (NiO_x) thin layer was successfully deposited on an n-Si (100) substrate by pulsed laser deposition (PLD), acting as a photoanode for efficient photo-oxidation of water under solar illumination. It was revealed that the formed n-Si/NiO_x heterojunction with good Schottky contact could improve photogenerated charge separation, and thus n-Si photoanodes deposited with a 105 nm-thick NiO_x electrocatalytic layer exhibited a photovoltage of ∼350 mV, leading to greatly improved photoelectrochemical performances for water oxidation. The stability of the photoanode was significantly enhanced with the increasing thickness of NiO_x protective layers. This study demonstrates a simple and...

  7. Weakly coupled bound states of Pauli operators

    Frank, Rupert L.; Morozov, Sergey; Vugalter, Semjon
    We consider the two-dimensional Pauli operator perturbed by a weakly coupled, attractive potential. We show that besides the eigenvalues arising from the Aharonov-Casher zero modes there are two or one (depending on whether the flux of the magnetic field is integer or not) additional eigenvalues for arbitrarily small coupling and we calculate their asymptotics in the weak coupling limit.

  8. Inequalities between Dirichlet and Neumann eigenvalues on the Heisenberg group

    Frank, Rupert L.; Laptev, Ari
    We prove that for any domain in the Heisenberg group the (k+1)'th Neumann eigenvalue of the sub-Laplacian is strictly less than the k'th Dirichlet eigenvalue. As a byproduct we obtain similar inequalities for the Euclidean Laplacian with a homogeneous magnetic field.

  9. Crossing the several scales of strain-accomplishing mechanisms in the hinterland of the central Andean fold–thrust belt, Bolivia

    McQuarrie, Nadine; Davis, George H.
    Depictions of structures at outcrop, regional and tectonic scales enforce horizontal shortening and vertical thickening as the predominant style of deformation at all scales within the hinterland of the central Andean fold–thrust belt. Outcrop-scale structures document a progression of strain that created: (1) flexural-slip folds, (2) fold flattening via axial-planar cleavage, (3) vertical stretching via boudinage and late-stage faulting and, finally, (4) kink folding. These examples of intraformational deformation are generally concentrated just beyond the tip lines of thrust faults, where fault-propagation folds and related structures are well developed. Fault-propagation folding accommodated the accrual of strain indicated by outcrop-scale structures...

  10. Representation of functions on big data associated with directed graphs

    Chui, Charles K.; Mhaskar, H. N.; Zhuang, Xiaosheng
    This paper is an extension of the previous work of Chui et al. (2015) [4], not only from numeric data to include non-numeric data as in that paper, but also from undirected graphs to directed graphs (called digraphs, for simplicity). Besides theoretical development, this paper introduces effective mathematical tools in terms of certain data-dependent orthogonal systems for function representation and analysis directly on the digraphs. In addition, this paper also includes algorithmic development and discussion of various experimental results on such data-sets as CORA, Proposition, and Wiki-votes.

  11. Dark gauge bosons: LHC signatures of non-Abelian kinetic mixing

    Argüelles, Carlos A.; He, Xiao-Gang; Ovanesyan, Grigory; Peng, Tao; Ramsey-Musolf, Michael J.
    We consider non-abelian kinetic mixing between the Standard Model SU(2)_L and a dark sector U(1)′ gauge group associated with the presence of a scalar SU(2)_L triplet. The magnitude of the resulting dark photon coupling ϵ is determined by the ratio of the triplet vacuum expectation value, constrained to by ≲4 GeV by electroweak precision tests, to the scale Λ of the effective theory. The corresponding effective operator Wilson coefficient can be O(1) while accommodating null results for dark photon searches, allowing for a distinctive LHC dark photon phenomenology. After outlining the possible LHC signatures, we illustrate by recasting current ATLAS...

  12. 3D nano-architected metallic glass: Size effect suppresses catastrophic failure

    Liontas, Rachel; Greer, Julia R.
    We investigate the mechanical behavior of 3D periodically architected metallic glass nanolattices, constructed from hollow beams of sputtered Zr-Ni-Al metallic glass. Nanolattices composed of beams with different wall thicknesses are fabricated by varying the sputter deposition time, resulting in nanolattices with median wall thicknesses of ∼88 nm, ∼57 nm, ∼38 nm, ∼30 nm, ∼20 nm, and ∼10 nm. Uniaxial compression experiments conducted inside a scanning electron microscope reveal a transition from brittle, catastrophic failure in thicker-walled nanolattices (median wall thicknesses of ∼88 and ∼57 nm) to deformable, gradual, layer-by-layer collapse in thinner-walled nanolattices (median wall thicknesses of ∼38 nm and...

  13. On acoustic wave beaming in two-dimensional structural lattices

    Zelhofer, Alex J.; Kochmann, Dennis M.
    We discuss directional energy flow, often referred to as wave beaming, in two-dimensional periodic truss lattices under infinitesimal harmonic excitation. While the phenomenon of directional wave guiding is well-known and commonly treated in the context of dispersion relations, the theoretical and computational tools to predict beaming are limited, which is why a fundamental understanding for complex lattices is incomplete. Here, we present a new strategy to identify partial band gaps and wave beaming in a simple fashion, covering wide frequency ranges and distinguishing in-plane and out-of-plane vibrational modes in lattices composed of linear elastic Euler-Bernoulli beams. By calculating group velocities...

  14. Experiments on imperfection insensitive axially loaded cylindrical shells

    Ning, Xin; Pellegrino, Sergio
    This paper presents an experimental study of imperfection insensitive composite wavy cylindrical shells subject to axial compression. A fabrication technique for making cylindrical shells with intricate shape of cross-sections has been developed. A photogrammetry technique to measure the geometric imperfections has also been developed. The behavior of the wavy shells under axial compression was predicted through simulations and measured through compression tests. Both the analyses and experiments have confirmed that the wavy shells are imperfection insensitive. Comparisons between the wavy shells and circular shells have also confirmed that introducing optimal symmetry-breaking wavy cross-sections can significantly reduce the imperfection sensitivity and...

  15. Time Resolved Study of Hydroxyl Radical Oxidation of Oleic Acid at the Air-Water Interface

    Zhang, Xinxing; Barraza, Kevin M.; Upton, Kathleen T.; Beauchamp, J. L.
    The ubiquity of oleic acid (OA) renders it a poster child for laboratory investigations of environmental oxidation chemistry. In the current study, mechanistic details of the oxidation of OA by hydroxyl radicals at the air-water interface are investigated using field-induced droplet ionization mass spectrometry (FIDI-MS). Products from OH oxidation of both unsaturated and saturated carbon atoms are identified, and mechanisms for both types of oxidation processes are proposed. Uptake of oxygen in the interfacial layer increases linearly with time, consistent with Langmuir-Hinshelwood reaction kinetics. These results provide fundamental knowledge relating to OH initiated degradation of fatty acids in atmospheric aerosols.

  16. Rotational energy transfer in collisions between CO and Ar at temperatures from 293 to 30 K

    Mertens, Laura A.; Labiad, Hamza; Denis-Alpizar, Otoniel; Fournier, Martin; Carty, David; Le Picard, Sébastien D.; Stoecklin, Thierry; Sims, Ian R.
    Experimental measurements and theoretical calculations are reported for rotational energy transfer in the Ar-CO system. Experiments were performed in cold uniform supersonic flows of Ar, using an infrared – vacuum ultraviolet double resonance technique to measure absolute state-to-state rate constants and total relaxation cross sections for rotational energy transfer within the (v = 2) vibrational state of CO in collision with Ar at temperatures from 30.5 to 293 K. Close-coupled calculations were also performed using a recent potential energy surface (Y. Sumiyoshi and Y. Endo, J. Chem. Phys. 142 (2015) 024314). Very good agreement is obtained between measured and calculated...

  17. Quantum Mechanics Reactive Dynamics Study of Solid Li-Electrode/Li_6PS_5Cl-Electrolyte Interface

    Cheng, Tao; Merinov, Boris V.; Morozov, Sergey I.; Goddard, William A., III
    Abstract We have performed a theoretical study of the Li/Li_6PS_5Cl interface and showed the ability of the applied computational methods to properly describe the chemical processes that occurs at the interface. After a 500 ps ab initio molecular dynamics simulation, we find that the Li/Li_6PS_5Cl interface decomposes with formation of multiple phases and the main decomposition products are Li_2S, Li_3P, LiCl, and possibly LiP. These findings are in good agreement with reported experimental data. The observed quick decomposition is attributed to the weak bonding between P and S. Basing on this and earlier obtained experimental results, we conclude that the...

  18. The Herschel Orion Protostar Survey: Luminosity and Envelope Evolution

    Fischer, William J.; Megeath, S. Thomas; Furlan, Elise; Ali, Babar; Stutz, Amelia M.; Tobin, John J.; Osorio, Mayra; Stanke, Thomas; Manoj, P.; Poteet, Charles A.; Booker, Joseph J.; Hartmann, Lee; Wilson, Thomas L.; Myers, Philip C.; Watson, Dan M.
    The Herschel Orion Protostar Survey obtained well-sampled 1.2–870 μm spectral energy distributions (SEDs) of over 300 protostars in the Orion molecular clouds, home to most of the young stellar objects (YSOs) in the nearest 500 pc. We plot the bolometric luminosities and temperatures for 330 Orion YSOs, 315 of which have bolometric temperatures characteristic of protostars. The histogram of the bolometric temperature is roughly flat; 29% of the protostars are in Class 0. The median luminosity decreases by a factor of four with increasing bolometric temperature; consequently, the Class 0 protostars are systematically brighter than the Class I protostars, with...

  19. Conservation of vibrational coherence in ultrafast electronic relaxation: The case of diplatinum complexes in solution

    Monni, Roberto; Auböck, Gerald; Kinschel, Dominik; Aziz-Lange, Kathrin M.; Gray, Harry B.; Vlček, Antonín; Chergui, Majed
    We report the results of ultrafast transient absorption studies of tetrakis(μ-pyrophosphito)diplatinate(II), [Pt_2(μ-P_2O_5H_2)_4]^(4−) (Pt(pop)) and its perfluoroborated derivative [Pt_2(μ-P_2O_5(BF_2)_4]^(4−) (Pt(pop-BF_2)) in water and acetonitrile upon excitation of high lying (<300 nm) UV absorption bands. We observe an ultrafast relaxation channel from high lying states to the lowest triplet state that partly (Pt(pop) in H_2O, Pt(pop-BF_2)) or fully (Pt(pop) in MeCN) bypasses the lowest singlet excited state. As a consequence, vibrational wave packets are detected in the lowest triplet state and/or the lowest excited singlet of both complexes, even though the electronic relaxation cascade spans ca. 2 and 1.3 eV, respectively. In...

  20. Measured Anxiety Affects Choices in Experimental "Clock" Games

    Kang, Min Jeong; Camerer, Colin
    We measure anxiety by skin conductance response (SCR) in an economic setting. In “clock” games, six agents receive private signals when an asset's price exceeds its fundamental value. They can sell for immediate value or wait to sell at a higher value. Waiting is risky because the price crashes to a lower value when three agents sell. Anxiety could lead people to sell too quickly when the game is played dynamically over time, compared to a static version with precommitted selling. Empirically, delays are shorter in dynamic games than in payoff-equivalent static games, and are associated with anxiety as measured.

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