Recursos de colección

Caltech Authors (169.428 recursos)

Repository of works by Caltech published authors.

Type = Book Section

Mostrando recursos 1 - 20 de 2.287

  1. Pedestrian Detection: A Benchmark

    Dollár, Piotr; Wojek, Christian; Schiele, Bernt; Perona, Pietro
    Pedestrian detection is a key problem in computer vision, with several applications including robotics, surveillance and automotive safety. Much of the progress of the past few years has been driven by the availability of challenging public datasets. To continue the rapid rate of innovation, we introduce the Caltech Pedestrian Dataset, which is two orders of magnitude larger than existing datasets. The dataset contains richly annotated video, recorded from a moving vehicle, with challenging images of low resolution and frequently occluded people. We propose improved evaluation metrics, demonstrating that commonly used per-window measures are flawed and can fail to predict performance...

  2. Speckle nulling wavefront control for Palomar and Keck

    Bottom, Michael; Femenia, Bruno; Huby, Elsa; Mawet, Dimitri; Dekany, Richard; Milburn, Jennifer; Serabyn, Eugene
    We present a speckle nulling code currently being used for high contrast imaging at the Palomar and Keck telescopes. The code can operate in open and closed loop and is self-calibrating, requiring no system model and minimal hand-coded parameters. Written in a modular fashion, it is straightforward to port to different instruments. It has been used with systems operating in the optical through thermal infrared, and can deliver nearly an order of magnitude improvement in raw contrast. We will be releasing this code to the public in the near future.

  3. VISIR Upgrade: all’s well that ends well

    Kerber, Florian; Käufl, Hans Ulrich; Tristram, Konrad; Asmus, Daniel; Baksai, Pedro; Di Lieto, Nicola; Dobrzycka, Danuta; Duhoux, Philippe; Finger, Gert; Hummel, Christian; Ives, Derek; Jakob, Gerd; Lundin, Lars; Mawet, Dimitri; Mehrgan, Leander; Moreau, Vincent; Pantin, Eric; Riquelme, Miguel; Sanchez, Joel; Sandrock, Stefan; Siebenmorgen, Ralf; Stegmaier, Jörg; Smette, Alain; Taylor, Julian; van den Acker, Mario; Valdes, Guillermo; Venema, Lars
    We present an overview of the VISIR instrument after its upgrade and return to science operations. VISIR is the midinfrared imager and spectrograph at ESO’s VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and ASTRON. The project plan was based on input from the ESO user community with the goal of enhancing the scientific performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As AQUARIUS detector array manufactured...

  4. High-contrast spectroscopy testbed for segmented telescopes

    Delorme, J. R.; Mawet, D.; Fucik, J.; Wallace, J. K.; Ruane, G.; Jovanovic, N.; Klimovich, N. S.; Llop Sayson, J. D.; Zhang, R.; Xin, Y.; Riddle, R.; Dekany, R.; Wang, J.; Choquet, E.; Xuan, W.; Encheverri, D.; Randolph, M.; Vasisht, G.; Mennesson, B.
    The High Contrast Spectroscopy Testbed for Segmented Telescopes (HCST) at Caltech is aimed at filling gaps in technology for future exoplanet imagers and providing the U.S. community with an academic facility to test components and techniques for high contrast imaging with future segmented ground-based telescope (TMT, E-ELT) and space-based telescopes (HabEx, LUVOIR). The HCST will be able to simulate segmented telescope geometries up to 1021 hexagonal segments and time-varying external wavefront disturbances. It also contains a wavefront corrector module based on two deformable mirrors followed by a classical 3-plane single-stage corona- graph (entrance apodizer, focal-plane mask, Lyot stop) and a...

  5. Fast and broadband detector for laser radiation

    Scorticati, Davide; Crapella, Giacomo; Pellegrino, Sergio
    We developed a fast detector (patent pending) based on the Laser Induced Transverse Voltage (LITV) effect. The advantage of detectors using the LITV effect over pyroelectric sensors and photodiodes for laser radiation measurements is the combination of an overall fast response time, broadband spectral acceptance, high saturation threshold to direct laser irradiation and the possibility to measure pulsed as well as cw-laser sources. The detector is capable of measuring the energy of single laser pulses with repetition frequencies up to the MHz range, adding the possibility to also measure the output power of cw-lasers. Moreover, the thermal nature of the...

  6. Phenomenological model for coupled multi-axial piezoelectricity

    Wei, Yuchen; Pellegrino, Sergio
    A quantitative calibration of an existing phenomenological model for polycrystalline ferroelectric ceramics is presented. The model relies on remnant strain and polarization as independent variables. Innovative experimental and numerical model identification procedures are developed for the characterization of the coupled electro-mechanical, multi-axial nonlinear constitutive law. Experiments were conducted on thin PZT-5A4E plates subjected to cross-thickness electric field. Unimorph structures with different thickness ratios between PZT-5A4E plate and substrate were tested, to subject the piezo plates to coupled electro-mechanical fields. Material state histories in electric field-strain-polarization space and stress-strain-polarization space were recorded. An optimization procedure is employed for the determination of...

  7. Chemical Characteristics of Sediments and Seawater

    Kump, Lee R.; Kuznetsov, Anton B.; Gorokhov, Igor M.; Melezhik, Victor A.; Farkaš, Juraj; Chakrabarti, Ramananda; Jacobsen, Stein B.; Reinhard, Christopher T.; Lyons, Timothy W.; Rouxel, Olivier; Asael, Dan; Dauphas, Nicolas; van Zuilen, Mark; Schoenberg, Ronny; Tissot, François L. H.; Hannah, Judith L.; Stein, Holly J.
    The transition from an anoxic to oxygenated atmosphere was arguably the most dramatic change in the history of the Earth. This “Great Oxidation Event” (Holland 2006) transformed the biogeochemical cycles of the elements by imposing an oxidative step in the cycles, creating strong redox gradients in the terrestrial and marine realms that energised microbial metabolism. Although much past research was focused on establishing when the rise of atmospheric oxygen took place, recognition that substantial mass-independent fraction (MIF) of the sulphur isotopes is restricted to the time interval before 2.45 Ga and requires an anoxic atmosphere (Farquhar et al. 2000, 2007;...

  8. Metrology camera system of prime focus spectrograph for Suburu telescope

    Wang, Shiang-Yu; Chou, Richard C. Y.; Huang, Pin-Jie; Ling, Hung-Hsu; Karr, Jennifer; Chang, Yin-Chang; Hu, Yen-Shan; Hsu, Shu-Fu; Chen, Hsin-Yo; Gunn, James E.; Reiley, Dan J.; Tamura, Naoyuki; Takato, Naruhisa; Shimono, Atsushi
    The Prime Focus Spectrograph (PFS) is a new optical/near-infrared multi-fiber spectrograph designed for the prime focus of the 8.2m Subaru telescope. PFS will cover a 1.3 degree diameter field with 2394 fibers to complement the imaging capabilities of Hyper SuprimeCam. To retain high throughput, the final positioning accuracy between the fibers and observing targets of PFS is required to be less than 10 microns. The metrology camera system (MCS) serves as the optical encoder of the fiber motors for the configuring of fibers. MCS provides the fiber positions within a 5 microns error over the 45 cm focal plane. The...

  9. Results of using permanent magnets to suppress Josephson noise in the KAPPa SIS receiver

    Wheeler, Caleb H.; Neric, Marko; Groppi, Christopher E.; Underhill, Matthew; Mani, Hamdi; Weinreb, Sander; Russell, Damon S.; Kooi, Jacob W.; Lichtenberger, Arthur W.; Walker, Christopher K.; Kulesa, Craig
    We present the results from the magnetic field generation within the Kilopixel Array Pathfinder Project (KAPPa) instrument. The KAPPa instrument is a terahertz heterodyne receiver using a Superconducting-Insulating- Superconducting (SIS) mixers. To improve performance, SIS mixers require a magnetic field to suppress Josephson noise. The KAPPa test receiver can house a tunable electromagnet used to optimize the applied magnetic field. The receiver is also capable of accommodating a permanent magnet that applies a fixed field. Our permanent magnet design uses off-the-shelf neodymium permanent magnets and then reshapes the magnetic field using machined steel concentrators. These concentrators allow the use of...

  10. Quantum-well-laser mirror degradation investigated by microprobe optical spectroscopy

    Corvasce, C.; Spagnolo, V.; Scamarcio, G.; Lugarà, M.; Adduci, F.; Ferrara, M.; Sibilano, M.; Pellegrino, S.; Del Guidice, M.; Re, M. G.
    A study of facet degradation of InGaAs quantum well lasers is reported. We tune up a Raman and photoluminescence micro-probe technique for determining the crystal structure and the temperature profile of the cladding layer, in steps of approximately 1 micrometer, with a temperature resolution better than 1 degree Kelvin. The cladding layer composition and cross- section temperature profile have been monitored during operation. A clear correlation between the facet degradation and the type of protective coating is found.

  11. Design of Al-free and Al-based InGaAs/GaAs strained quantum well 980-nm pump lasers including thermal behavior effects on E/O characteristics

    Pellegrino, S.; Re, M. G.; Beoni, C.; Reichenbach, D.; Vidimari, F.
    A 2D thermal simulator and a model to evaluate high power lasers characteristics have been developed. With these models it was possible to optimize cavity length of InGaAs/GaAs (Multiple) Quantum Well 980 nm lasers realized both with Al-based and Al-free confining layers. A comprehensive experimental investigation of the influence of cavity length and temperature on the laser emission wavelength has been performed. This allows a fine trimming of the devices to match the Erbium doped fiber absorption bandwidth.

  12. The iNaturalist Species Classification and Detection Dataset

    Van Horn, Grant; Mac Aodha, Oisin; Song, Yang; Cui, Yin; Sun, Chen; Shepard, Alex; Adam, Hartwig; Perona, Pietro; Belongie, Serge
    Existing image classification datasets used in computer vision tend to have a uniform distribution of images across object categories. In contrast, the natural world is heavily imbalanced, as some species are more abundant and easier to photograph than others. To encourage further progress in challenging real world conditions we present the iNaturalist species classification and detection dataset, consisting of 859,000 images from over 5,000 different species of plants and animals. It features visually similar species, captured in a wide variety of situations, from all over the world. Images were collected with different camera types, have varying image quality, feature a...

  13. Evaluation of Features Detectors and Descriptors based on 3D objects

    Moreels, Pierre; Perona, Pietro
    We explore the performance of a number of popular feature detectors and descriptors in matching 3D object features across viewpoints and lighting conditions. To this end we design a method, based on intersecting epipolar constraints, for providing ground truth correspondence automatically. We collect a database of 100 objects viewed from 144 calibrated viewpoints under three different lighting conditions. We find that the combination of Hessian-affine feature finder and SIFT features is most robust to viewpoint change. Harris-affine combined with SIFT and Hessian-affine combined with shape context descriptors were best respectively for lighting changes and scale changes. We also find that...

  14. Motion Estimation via Dynamic Vision

    Soatto, Stefano; Perona, Pietro; Frezza, Ruggero; Picci, Gorgio
    Estimating the 3D motion of an object from a sequence of projections is of paramount importance in a variety of applications in control and robotics. Although "visual motion estimation" is an old problem, only recently tools from control and estimation theory have hinted at acceptable solutions. Moreover, the problem raises a number of issues of system theoretic interest, such as nonlinear estimation and identification on topological manifolds and observability in a projective geometric framework. In this paper we analyze a formulation of the visual motion estimation problem in terms of identification of nonlinear implicit systems with parameters on the so-called...

  15. A Current-Mode Position Sensitive Circuit

    Tartagni, Marco; Perona, Pietro
    A novel technique to implement mesh-type position sensitive devices using current-mode analog VLSI is presented. By taking advantage of local analog computation this approach allows to create extremely compact circuit implementations. While in conventional approaches most sensor characteristics are adjusted by setting process parameters, our technique is fully electronically tunable and suitable to be implemented in general purpose CMOS technology. We have verified experimentally our idea designing and fabricating via MOSIS a 20 element 1D position circuit. Test results are presented demonstrating nonlinearity below 2.2% for currents in the range of 5pA to 10nA.

  16. Caenorhabditis nomenclature

    Tuli, Mary Ann; Daul, Aric; Schedl, Tim
    Genetic nomenclature for Caenorhabditis species and other nematodes is supervised by WormBase in collaboration with the Caenorhabditis Genetics Center (CGC) and with essential input from the community of scientists working on C. elegans and other nematodes.

  17. A Note on Helson’s Conjecture on Moments of Random Multiplicative Functions

    Harper, Adam J.; Nikeghbali, Ashkan; Radziwiłł, Maksym
    In this note we are interested in cancellations in sums of multiplicative functions. It is well known that M(x) := Σ n≤x µ(n) = 0(x^(1/2+ε) is equivalent to the Riemann Hypothesis. On the other hand, it is also a classical result that M(x) > x^(1/2+ε) for a sequence of arbitrarily large x. It is in fact conjectured that lim x→ ∞ M(x)/ √x(log log log x)^(5/4) = ±B for some constant B > 0 (see [21]).

  18. A Degenerate Optical Parametric Oscillator Network for Coherent Computation

    Wang, Zhe; Marandi, Alireza; Takata, Kenta; Byer, Robert L.; Yamamoto, Yoshihisa
    Laws of physics have proved useful for solving combinatorial optimization problems. This chapter introduces a network of degenerate optical parametric oscillators which takes advantage of principles of quantum optics to tackle NP-hard problems. The underlying mechanism originates from the bistability of the output phase of each oscillator, coherent interactions between coupled oscillators, and the inherent preference of the network for oscillating in a mode with the minimum photon loss. Computational experiments have been extensively performed using instances of an NP-hard problem in graph theory with the number of vertices ranging from 4 to 20000. The numerical results clearly demonstrate the...

  19. Incorporation of Non-Canonical Amino Acids into Proteins by Global Reassignment of Sense Codons

    Fang, Katharine Y.; Lieblich, Seth A.; Tirrell, David A.
    Non-canonical amino acids are finding increasing use in basic and applied research. Proteins that evolved naturally for biological function did so by exploiting the chemistries of the canonical amino acids; however, when proteins are repurposed for biomedical and pharmacological applications, they are often subject to conditions different from those characteristic of their original biological environments. Non-canonical amino acids can impart properties that are inaccessible within canonical protein sequence space, and can thereby lead to improved or new functionality. We describe simple methods for global replacement of canonical amino acids by their non-canonical counterparts in recombinant proteins made in high yield...

  20. Optical Imaging of Vibrationally-Tagged Small molecules for Biomedicine

    Wei, Lu; Min, Wei
    We report a novel imaging platform, by coupling stimulated Raman scattering microscopy with small vibrational tags (including isotopes and alkynes), to probe dynamics of small biomolecules in living organisms with superb sensitivity, specificity and biocompatibility.

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.