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Caltech Authors (169.428 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 24.318

  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. Sensitivity and discovery potential of the proposed nEXO experiment to neutrinoless double-β decay

    Albert, J. B.; Vogel, P.
    The next-generation Enriched Xenon Observatory (nEXO) is a proposed experiment to search for neutrinoless double-β (0νββ) decay in ^(136)Xe with a target half-life sensitivity of approximately 10^(28) yr using 5×10^3 kg of isotopically enriched liquid-xenon in a time projection chamber. This improvement of two orders of magnitude in sensitivity over current limits is obtained by a significant increase of the ^(136)Xe mass, the monolithic and homogeneous configuration of the active medium, and the multiparameter measurements of the interactions enabled by the time projection chamber. The detector concept and anticipated performance are presented based upon demonstrated realizable background rates.

  3. 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.

  4. 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...

  5. 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...

  6. Motivations of educators for participating in an authentic astronomy research experience professional development program

    Rebull, L. M.; Roberts, T.; Laurence, W.; Fitzgerald, M. T.; French, D. A.; Gorjian, V.; Squires, G. K.
    [This paper is part of the Focused Collection on Astronomy Education Research.] The NASA/IPAC Teacher Archive Research Program (NITARP) partners small groups of educators with a research astronomer for a year-long authentic research project. This program aligns well with the characteristics of high-quality professional development (PD) programs and has worked with a total of 103 educators since 2005. In this paper, surveys were explored that were obtained from 74 different educators, at up to four waypoints during the course of 13 months, incorporating data from the class of 2010 through the class of 2017. This paper investigates how participating teachers...

  7. Defining the baseline of the REE stable isotope variations in solar system materials: Earth

    Hu, J. Y.; Tissot, F. L. H.; Yokochi, R.; Ireland, T. J.; Dauphas, N.
    Mass-dependent fractionations (MDFs) of stable isotopes record critical information regarding the origin and evolution of planetary materials [1]. Studies of MDF of refractory lithophile elements (RLEs) can provide insights into condensation/evaporation and planetary accretion processes in the early solar system. For example, the lighter calcium isotope composition observed in carbonaceous meteorites compared to that of the bulk silicate Earth, enstatite and ordinary chondrites [2, 3] may be due to the contribution of refractory dust [4, 5], which has a light Ca isotope composition [6, 7]. In contrast, titanium, another RLE with a similar chemical behavior in the early solar system, was found to have uniform isotope compositions among different groups...

  8. ^(36)Cl-^(36)S in Allende CAIs: Implication for the origins of ^(36)Cl in the early solar system

    Tang, H.; Liu, M-C.; McKeegan, K. D.; Tissot, F. L. H.; Dauphas, N.
    Chlorine-36 (t_(1/2)=0.3 Myr) decays to either ^(36)Ar (98%, β-) or ^(36)S (1.9%, ε and β+). This radionuclide can be produced by either charged particle irradiation [1,2] or stellar nucleosynthesis [3]. Evidence for the prior existence of ^(36)Cl in the Early Solar System (ESS) comes from radiogenic excesses of ^(36)Ar [4,5] and/or ^(36)S [6-9] in secondary phases (e.g., sodalite and wadalite) of ESS materials such as Ca, Al-rich inclusions (CAIs) and chondrules. However, the inferred initial ^(36)Cl/^(35)Cl ratios vary over three orders of magnitude among different chondrite constituents (5×10^(-6)-9×10^(-3)) [6-9]. Interestingly, although the initial ^(36)Cl/^(35)Cl ratios inferred in previous studies vary widely, all secondary phases...

  9. Uranium isotope variations in group II refractory inclusions

    Tissot, F. L. H.; Dauphas, N.; Grossman, L.
    The ^(235)U/^(238)U ratio shows little variability in most terrestrial and meteoritic bodies (≤1 ‰) [1-3]. In contrast, large excesses of ^(235)U, up to 3.5 ‰, have been found in a few Calcium-Aluminum rich inclusions (CAIs) and have been interpreted as evidence of live ^(247)Cm (t_(1/2) = 15.6 My) in the early solar system (SS) [4]. Though this is a plausible explanation, it relies on four points with high Nd/U ratio that define a “pseudochron”, so more work is needed to determine the cause of U isotope variations in CAIs. Here, we report some preliminary results on the identification, characterization and U isotopic analysis of 12 fine-grained, group II, CAIs from the Allende...

  10. Introducing Teflon-HPLC

    Tissot, F. L. H.; Ireland, T. J.; Yokochi, R.; Dauphas, N.
    With increasingly ambitious sample return missions and instrumentation of ever-increasing sensitivity and precision, column chromatography appears to be the neglected step-child of isotope geochemistry and little improvement has been brought to it in the past few decades. Traditional column chromatography (i.e., open-system, gravity driven) techniques suffer from significant limitations pertaining to the overall length of column, resin size and diffusion effects, which can severely compromise separation efficiencies. Furthermore, some fine-scale separations still require complicated multi-step, highly time-consuming protocols (e.g. Ni-Mg, [1]). High-performance liquid chromatography (HPLC), while overcoming many of these limitations (e.g. a closed-system setup; the ability to pressurize the system,...

  11. 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...

  12. 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...

  13. ^(238)U/^(235)U in marine carbonates as a tracer of Precambrian paleoredox conditions

    Chen, C.; Tissot, F. L. H.; Dauphas, N.; Bekker, A.; Halverson, G. P.; Veizer, J.
    The timing and magnitude of the oxygenation of Earth’s ocean is still a matter of intense debate. Previous work suggested that the uranium isotope variations recorded in ancient marine sediments, such as shales and carbonates, could provide valuable insights into paleoredox conditions [e.g., 1-11]. In this work, we study U concentration and isotopic composition of a large number of Precambrian carbonates to place constraints on long-term variations in oceanic redox conditions.

  14. Establishing the liquid phase equilibrium of angrites to constrain their petrogenesis

    Tissot, F. L. H.; Collinet, M.; Dauphas, N.; Grove, T. L.
    Angrites are a series of differentiat-ed meteorites, extremely silica undersaturated and with unusally high Ca and Al contents [1]. They are thought to originate from a small planetesimal parent body of ~ 100-200 km in radius ([2-3]), can be either plutonic (i.e., cumulates) or volcanic (often referred to as quenched) in origin, and their old formation ages (4 to 11 Myr after CAIs) have made them prime anchors to tie the relative chronologies inferred from short-lived radionuclides (e.g., Al-Mg, Mn-Cr, Hf-W) to the absolute Pb-Pb clock [4]. They are also the most vola-tile element-depleted meteorites available, displaying a K-depletion of...

  15. Developments in PF-HPLC (pneumatic-fluoropolymer high performance liquid chromatography)

    Hu, J. Y.; Tissot, F. L. H.; Yokochi, R.; Ireland, T. J.; Dauphas, N.
    Return missions are providing unique opportunities to deepen our knowledge of the formation and evolution of the solar system. The six Apollo missions have been critical in shaping our understanding of the Earth-Moon history [1], and the recent Genesis (solar wind; e.g., [2]), Stardust (cometary dust from Wild 2; e.g., [3,4]) and Hayabusa (dust from S-type asteroid from Itokawa; e.g., [5]) missions brought in a wealth of data.

  16. I-Xe studies of aqueous alteration in the Allende CAI Curious Marie

    Pravdivtseva, O.; Meshik, A.; Tissot, F. L. H.; Dauphas, N.
    The Allende fine-grained inclusion Curious Marie is a unique CAI. It is depleted in uranium but contains large ^(235)U excess [1], providing new evidence that ^(247)Cm was alive in the Early Solar System, as has been previously suggested [2], and leading to an updated (^(247)Cm/^(235)U)initial ratio of (1.1±0.3)×10^(-4).

  17. The REE isotopic compositions of the Earth

    Hu, J. Y.; Dauphas, N.; Tissot, F. L. H.; Yokochi, R.; Ireland, T. J.
    Lanthanides are a group of 14 naturally occurring elements with atomic numbers ranging from 57 (La) to 74 (Lu), which are also known as rare earth elements (REE). REEs are ubiquitous in minerals and rocks. The chemical properties of REEs vary as smooth functions of their atomic numbers, a phenomenon known as the contraction of the lanthanides. This is the main control behind REE fractionation in minerals and rocks. The relative abundance of REEs is usually presented as the REE pattern by normalizing the concentrations in the sample to those in reference materials such as chondrites and shales.

  18. SN 2017ein and the Possible First Identification of a Type Ic Supernova Progenitor

    Van Dyk, Schuyler D.; Zheng, WeiKang; Brink, Thomas G.; Filippenko, Alexei V.; Milisavljevic, Dan; Andrews, Jennifer E.; Smith, Nathan; Cignoni, Michele; Fox, Ori D.; Kelly, Patrick L.; Adamo, Angela; Yunus, Sameen; Zhang, Keto; Kumar, Sahana
    We have identified a progenitor candidate in archival Hubble Space Telescope (HST) images for the Type Ic supernova (SN Ic) SN 2017ein in NGC 3938, pinpointing the candidate's location via HSTTarget of Opportunity imaging of the SN itself. This would be the first identification of a stellar-like object as a progenitor candidate for any SN Ic to date. We also present observations of SN 2017ein during the first ~49 days since explosion. We find that SN 2017ein most resembles the well-studied SN Ic SN 2007gr. We infer that SN 2017ein experienced a total visual extinction of A_V ≈ 1.0–1.9 mag,...

  19. Single-breath-hold photoacoustic computed tomography of the breast

    Lin, Li; Hu, Peng; Shi, Junhui; Appleton, Catherine M.; Maslov, Konstantin; Li, Lei; Zhang, Ruiying; Wang, Lihong V.
    We have developed a single-breath-hold photoacoustic computed tomography (SBH-PACT) system to reveal detailed angiographic structures in human breasts. SBH-PACT features a deep penetration depth (4 cm in vivo) with high spatial and temporal resolutions (255 µm in-plane resolution and a 10 Hz 2D frame rate). By scanning the entire breast within a single breath hold (~15 s), a volumetric image can be acquired and subsequently reconstructed utilizing 3D back-projection with negligible breathing-induced motion artifacts. SBH-PACT clearly reveals tumors by observing higher blood vessel densities associated with tumors at high spatial resolution, showing early promise for high sensitivity in radiographically dense breasts. In addition to...

  20. Light Curves of Hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory

    De Cia, Annalisa; Yan, Lin; Kasliwal, M. M.
    We investigate the light-curve properties of a sample of 26 spectroscopically confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar Transient Factory survey. These events are brighter than SNe Ib/c and SNe Ic-BL, on average, by about 4 and 2 mag, respectively. The peak absolute magnitudes of SLSNe-I in rest-frame g band span −22 ≾ M g ≾ −20 mag, and these peaks are not powered by radioactive ^(56)Ni, unless strong asymmetries are at play. The rise timescales are longer for SLSNe than for normal SNe Ib/c, by roughly 10 days, for events with similar decay times. Thus, SLSNe-I can be...

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