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Caltech Authors (136.887 recursos)

Repository of works by Caltech published authors.

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  1. Rapid Assessment of Earthquake Source Characteristics

    Lui, Semechah K. Y.; Helmberger, Don; Yu, Junjie; Wei, Shengji
    Recent studies emphasize the rapid assessment of earthquake source properties, such as moment magnitude, to help alleviate the impact of earthquakes. Depending on local crustal structure, earthquakes occurring at different depths can differ greatly in high‐frequency motions, which emphasizes the importance in constraining focal depth for the predictions of strong motions. For large earthquakes, assessing rupture directivity is also essential in estimating ground‐motion effects throughout the source region. In this article, we perform an in‐depth study on a group of recent earthquakes near the intersection of the San Jacinto and San Andreas fault systems in southern California. We develop a...

  2. Molecular Control of Flower Development

    Vishnevetsky, M.; Meyerowitz, E. M.
    The last decade has been an exciting period in plant molecular biology in general and in molecular studies of flower development in particular. The isolation of the first floral meristem identity and floral homeotic genes of Arabidopsis in the late 1980s—early ‘80s opened the way to in-depth studies of molecular aspects of floral development (Bowman et al., 1989; Coen et al., 1990; Sommer et al., 1990; Yanofsky et al., 1990). These investigations have led to insights into inflorescence and flower development in higher eudicotyledonous flowering plants, using mainly the predominant model of Arabidopsis thaliana (thale cress). The abundance of mutants,...

  3. Modeling the organization of the WUSCHEL expression domain in the shoot apical meristem

    Jönsson, Henrik; Heisler, Marcus; Reddy, G. Venugopala; Agrawal, Vikas; Gor, Victoria; Shapiro, Bruce E.; Mjolsness, Eric; Meyerowitz, Elliot M.
    Motivation: The above-ground tissues of higher plants are generated from a small region of cells situated at the plant apex called the shoot apical meristem. An important genetic control circuit modulating the size of the Arabidopsis thaliana meristem is a feed-back network between the CLAVATA3 and WUSCHEL genes. Although the expression patterns for these genes do not overlap, WUSCHEL activity is both necessary and sufficient (when expressed ectopically) for the induction of CLAVATA3 expression. However, upregulation of CLAVATA3 in conjunction with the receptor kinase CLAVATA1 results in the downregulation of WUSCHEL. Despite much work, experimental data for this network are...

  4. Contrasting cloud composition between coupled and decoupled marine boundary layer clouds

    Wang, Zhen; Ramirez, Marco Mora; Dadashazar, Hossein; MacDonald, Alex B.; Crosbie, Ewan; Bates, Kelvin H.; Coggon, Matthew M.; Craven, Jill S.; Lynch, Peng; Campbell, James R.; Aghdam, Mojtaba Azadi; Woods, Roy K.; Jonsson, Haflidi; Flagan, Richard C.; Seinfeld, John H.; Sorooshian, Armin
    Marine stratocumulus clouds often become decoupled from the vertical layer immediately above the ocean surface. This study contrasts cloud chemical composition between coupled and decoupled marine stratocumulus clouds for dissolved nonwater substances. Cloud water and droplet residual particle composition were measured in clouds off the California coast during three airborne experiments in July–August of separate years (Eastern Pacific Emitted Aerosol Cloud Experiment 2011, Nucleation in California Experiment 2013, and Biological and Oceanic Atmospheric Study 2015). Decoupled clouds exhibited significantly lower air-equivalent mass concentrations in both cloud water and droplet residual particles, consistent with reduced cloud droplet number concentration and subcloud...

  5. Colour formation on the wings of the butterfly Hypolimnas salmacis by scale stacking

    Siddique, Radwanul Hasan; Vignolini, Silvia; Bartels, Carolin; Wacker, Irene; Hölscher, Hendrik
    The butterfly genus Hypolimnas features iridescent blue colouration in some areas of its dorsal wings. Here, we analyse the mechanisms responsible for such colouration on the dorsal wings of Hypolimnas salmacis and experimentally demonstrate that the lower thin lamina in the white cover scales causes the blue iridescence. This outcome contradicts other studies reporting that the radiant blue in Hypolimnas butterflies is caused by complex ridge-lamellar architectures in the upper lamina of the cover scales. Our comprehensive optical study supported by numerical calculation however shows that scale stacking primarily induces the observed colour appearance of Hypolimnas salmacis.

  6. The Dynamic Free Rider Problem: A Laboratory Study

    Battaglini, Marco; Nunnari, Salvatore; Palfrey, Thomas R.
    We report the results of an experiment that investigates free riding in the accumulation of durable public goods. We consider economies with reversibility, where contributions can be positive or negative; and economies with irreversibility, where contributions are nonnegative. Aggregate outcomes support the qualitative predictions of the Markov Perfect Equilibria (MPE) characterized in Battaglini, Nunnari, and Palfrey (2014): steady state levels of public good are lower with reversibility than irreversibility; accumulation is inefficiently slow; and the public good is under-provided in both regimes. On the other hand, public good levels are higher than MPE, and some evidence of history dependence is...

  7. Motion-corrected Fourier ptychography

    Bian, Liheng; Zheng, Guoan; Guo, Kaikai; Suo, Jinli; Yang, Changhuei; Chen, Feng; Dai, Qionghai
    Fourier ptychography (FP) is a recently proposed computational imaging technique for high space-bandwidth product imaging. In real setups such as endoscope and transmission electron microscope, the common sample motion largely degrades the FP reconstruction and limits its practicability. In this paper, we propose a novel FP reconstruction method to efficiently correct for unknown sample motion. Specifically, we adaptively update the sample’s Fourier spectrum from low spatial-frequency regions towards high spatial-frequency ones, with an additional motion recovery and phase-offset compensation procedure for each sub-spectrum. Benefiting from the phase retrieval redundancy theory, the required large overlap between adjacent sub-spectra offers an accurate...

  8. The AIROPA software package - Milestones for testing general relativity in the strong gravity regime with AO

    Witzel, Gunther; Lu, Jessica R.; Ghez, Andrea M.; Martinez, Gregory D.; Fitzgerald, Michael P.; Britton, Matthew; Sitarski, Breann N.; Do, Tuan; Campbell, Randall D.; Service, Maxwell; Matthews, Keith; Morris, Mark R.; Becklin, E. E.; Wizinowich, Peter L.; Ragland, Sam; Doppmann, Greg; Neyman, Chris; Lyke, James; Kassis, Marc; Rizzi , Luca; Lilley, Scott; Rampy, Rachel
    General relativity can be tested in the strong gravity regime by monitoring stars orbiting the supermassive black hole at the Galactic Center with adaptive optics. However, the limiting source of uncertainty is the spatial PSF variability due to atmospheric anisoplanatism and instrumental aberrations. The Galactic Center Group at UCLA has completed a project developing algorithms to predict PSF variability for Keck AO images. We have created a new software package (AIROPA), based on modified versions of StarFinder and Arroyo, that takes atmospheric turbulence profiles, instrumental aberration maps, and images as inputs and delivers improved photometry and astrometry on crowded fields....

  9. Thirty Meter Telescope Narrow Field InfraRed Adaptive Optics System Real-Time Controller Prototyping Results

    Smith, Malcolm; Kerley, Dan; Chapin, Edward L.; Dunn, Jennifer; Herriot, Glen; Véran, Jean-Pierre; Boyer, Corinne; Ellerbroek, Brent; Gilles, Luc; Wang, Lianqi
    Prototyping and benchmarking was performed for the Real-Time Controller (RTC) of the Narrow Field InfraRed Adaptive Optics System (NFIRAOS). To perform wavefront correction, NFIRAOS utilizes two deformable mirrors (DM) and one tip/tilt stage (TTS). The RTC receives wavefront information from six Laser Guide Star (LGS) Shack- Hartmann WaveFront Sensors (WFS), one high-order Natural Guide Star Pyramid WaveFront Sensor (PWFS) and multiple low-order instrument detectors. The RTC uses this information to determine the commands to send to the wavefront correctors. NFIRAOS is the first light AO system for the Thirty Meter Telescope (TMT). The prototyping was performed using dual-socket high performance Linux...

  10. The statistics of atmospheric turbulence at Maunakea measured by RAVEN

    Ono, Y. H.; Correia, Carlos M.; Lardiére, O.; Andersen, D. R.; Oya, S.; Akiyama, M.; Gamroth, D.; Jackson, K.; Martin, O.; Guesalaga, A.; Bradley, C.
    Prior statistical knowledge of the turbulence such as turbulence strength, layer altitudes and the outer scale is essential for atmospheric tomography in adaptive-optics (AO). These atmospheric parameters can be estimated from measurements of multiple Shack-Hartmann wave-front sensors (SH-WFSs) by the SLOpe Detection And Ranging (SLODAR). In this paper, we present the statistics of the vertical CN^2 and the outer scale L_0 at Maunakea in Hawaii estimated from 60 hours telemetry data in total from multiple SH-WFSs of RAVEN, which is an on-sky multi-object AO demonstrator tested on the Subaru telescope. The mean seeing during the RAVEN on-sky observations is 0.475...

  11. Robo-AO Kitt Peak: Status of the system and deployment of a sub-electron readnoise IR camera to detect low-mass companions

    Salama, Maïssa; Baranec, Christoph; Jensen-Clem, Rebecca; Riddle, Reed; Duev, Dmitry; Kulkarni, Shrinivas; Law, Nicholas M.
    We have started an initial three-year deployment of Robo-AO at the 2.1-m telescope at Kitt Peak, Arizona as of November 2015. We report here on the project status and two new developments with the Robo-AO KP system: the commissioning of a sub-electron readnoise SAPHIRA near-infrared camera, which will allow us to widen the scope of possible targets to low-mass stellar and substellar objects; and, performance analysis and tuning of the adaptive optics system, which will improve the sensitivity to these objects. Commissioning of the near-infrared camera and optimizing the AO performance occur in parallel with ongoing visible-light science programs.

  12. Keck II Laser Guide Star AO System and Performance with the TOPTICA/MPBC Laser

    Chin, Jason C. Y.; Wizinowich, Peter; Wetherell, Ed; Lilley, Scott; Cetre, Sylvain; Ragland, Sam; Medeiros, Drew; Tsubota, Kevin; Doppmann, Greg; Otarola, Angel; Wei, Kai
    The Keck II Laser Guide Star (LGS) Adaptive Optics (AO) System was upgraded from a dye laser to a TOPTICA/MPBC Raman-Fibre Amplification (RFA) laser in December 2015. The W. M. Keck Observatory (WMKO) has been operating its AO system with a LGS for science since 2004 using a first generation 15 W dye laser. Using the latest diode pump laser technology, Raman amplification, and a well-tuned second harmonic generator (SHG), this Next Generation Laser (NGL) is able to produce a highly stable 589 nm laser beam with the required power, wavelength and mode quality. The beam’s linear polarization and continuous...

  13. Analysis of Flow Timescales on a Periodically Pitching/Surging Airfoil

    Dunne, R.; Schmid, P. J.; McKeon, B. J.
    Time-resolved velocity fields around a pitching and surging NACA 0018 airfoil were analyzed to investigate the influence of three independent timescales associated with the unsteady flowfield. The first of these timescales, the period of the pitch/surge motion, is directly linked to the development of dynamic stall. A simplified model of the flow using only a time constant mode and the first two harmonics of the pitch surge frequency has been shown to accurately model the flow. Full stall and leading-edge flow separation, however, were found to take place before the maximum angle of attack, indicating that a different timescale was...

  14. The Rapid Transient Surveyor

    Baranec, Christoph; Lu, J. R.; Wright, S. A.; Tonry, J.; Tully, R. B.; Szapudi, I.; Takamiya, M.; Hunter, L.; Riddle, R.; Chen, S.; Chun, M.
    The Rapid Transient Surveyor (RTS) is a proposed rapid-response, high-cadence adaptive optics (AO) facility for the UH 2.2-m telescope on Maunakea. RTS will uniquely address the need for high-acuity and sensitive near-infrared spectral follow-up observations of tens of thousands of objects in mere months by combining an excellent observing site, unmatched robotic observational efficiency, and an AO system that significantly increases both sensitivity and spatial resolving power. We will initially use RTS to obtain the infrared spectra of ∼4,000 Type Ia supernovae identified by the Asteroid Terrestrial-Impact Last Alert System over a two year period that will be crucial to...

  15. Approximate sorting of data streams with limited storage

    Farnoud, Farzad; Yaakobi, Eitan; Bruck, Jehoshua
    We consider the problem of approximate sorting of a data stream (in one pass) with limited internal storage where the goal is not to rearrange data but to output a permutation that reflects the ordering of the elements of the data stream as closely as possible. Our main objective is to study the relationship between the quality of the sorting and the amount of available storage. To measure quality, we use permutation distortion metrics, namely the Kendall tau, Chebyshev, and weighted Kendall metrics, as well as mutual information, between the output permutation and the true ordering of data elements. We...

  16. Deep vs. shallow networks: An approximation theory perspective

    Mhaskar, Hrushikesh N.; Poggio, Tomaso
    The paper briefly reviews several recent results on hierarchical architectures for learning from examples, that may formally explain the conditions under which Deep Convolutional Neural Networks perform much better in function approximation problems than shallow, one-hidden layer architectures. The paper announces new results for a non-smooth activation function — the ReLU function — used in present-day neural networks, as well as for the Gaussian networks. We propose a new definition of relative dimension to encapsulate different notions of sparsity of a function class that can possibly be exploited by deep networks but not by shallow ones to drastically reduce the...

  17. The Robo-AO KOI survey: laser adaptive optics imaging of every Kepler exoplanet candidate

    Ziegler, Carl; Law, Nicholas M.; Baranec, Christoph; Morton, Tim; Riddle, Reed; Atkinson, Dani; Nofi, Larissa
    The Robo-AO Kepler Planetary Candidate Survey is observing every Kepler planet candidate host star (KOI) with laser adaptive optics imaging to hunt for blended nearby stars which may be physically associated companions. With the unparalleled efficiency provided by the first fully robotic adaptive optics system, we perform the critical search for nearby stars (0.15" to 4.0" separation with contrasts up to 6 magnitudes) that dilute the observed planetary transit signal, contributing to inaccurate planetary characteristics or astrophysical false positives. We present 3313 high resolution observations of Kepler planetary hosts from 2012-2015, discovering 479 nearby stars. We measure an overall nearby...

  18. Massively Parallelized Simulation of Deflagration-to-Detonation Transition in a Konvoi-Type Pressurized Water Reactor

    Hasslberger, Josef; Katzy, Peter; Sattelmayer, Thomas; Boeck, Lorenz R.
    For the purpose of nuclear safety analysis, a reactive flow solver has been developed to determine the hazard potential of large-scale hydrogen explosions. Without using empirical transition criteria, the whole combustion process (including DDT) is computed within a single solver framework. In this paper, we present massively parallelized three-dimensional explosion simulations in a full-scale pressurized water reactor of the Konvoi type. Several generic DDT scenarios in globally lean hydrogen-air mixtures are examined to assess the importance of different input parameters. It is demonstrated that the explosion process is highly sensitive to mixture composition, ignition location and thermodynamic initial conditions. Pressure...

  19. Leading Edge Vortex Development on Pitching and Surging Airfoils: A Study of Vertical Axis Wind Turbines

    Dunne, Reeve; Tsai, Hsieh-Chen; Colonius, Tim; McKeon, Beverley J.
    Vertical axis wind turbine blades undergo dynamic stall due to the large angle of attack variation they experience during a turbine rotation. Particle image velocimetry on a pitching and surging airfoil was used to perform time resolved measurements at blade Reynolds numbers near turbine operating conditions of 10^5. These experiments were compared to simulations performed in the rotating turbine frame as well as the linear, experimental, frame at a Reynolds number of 10^3 to investigate rotational and Reynolds number effects. The flow was shown to develop similarly prior to separation, but the kinematics of vortices shed post separation were reference...

  20. Transitional annealed adaptive slice sampling for Gaussian process hyper-parameter estimation

    Garbuno-Inigo, Alfredo; DiazDelaO, F. A.; Zuev, Konstantin M.
    Surrogate models have become ubiquitous in science and engineering for their capability of emulating expensive computer codes, necessary to model and investigate complex phenomena. Bayesian emulators based on Gaussian processes adequately quantify the uncertainty that results from the cost of the original simulator, and thus the inability to evaluate it on the whole input space. However, it is common in the literature that only a partial Bayesian analysis is carried out, whereby the underlying hyper-parameters are estimated via gradient-free optimization or genetic algorithms, to name a few methods. On the other hand, maximum a posteriori (MAP) estimation could discard important...

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