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Caltech Authors (158.172 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 13.344

  1. Search for top quark partners with charge 5/3 in proton-proton collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Lawhorn, J. M.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    A search for the production of heavy partners of the top quark with charge 5/3 (X_(5/3)) decaying into a top quark and a W boson is performed with a data sample corresponding to an integrated luminosity of 2.3 fb^(−1), collected in proton-proton collisions at a center-of-mass energy of 13 TeV with the CMS detector at the CERN LHC. Final states with either a pair of same-sign leptons or a single lepton, along with jets, are considered. No significant excess is observed in the data above the expected standard model background contribution and an X_(5/3) quark with right-handed (left-handed) couplings is...

  2. Analysis of the potential for non-invasive imaging of oxygenation at heart depth, using ultrasound optical tomography (UOT) or photo-acoustic tomography (PAT)

    Walther, Andreas; Rippe, Lars; Wang, Lihong V.; Andersson-Engels, Stefan; Kröll, Stefan
    Despite the important medical implications, it is currently an open task to find optical non-invasive techniques that can image deep organs in humans. Addressing this, photo-acoustic tomography (PAT) has received a great deal of attention in the past decade, owing to favorable properties like high contrast and high spatial resolution. However, even with optimal components PAT cannot penetrate beyond a few centimeters, which still presents an important limitation of the technique. Here, we calculate the absorption contrast levels for PAT and for ultrasound optical tomography (UOT) and compare them to their relevant noise sources as a function of imaging depth....

  3. The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. I. Discovery of the Optical Counterpart Using the Dark Energy Camera

    Soares-Santos, M.; Eifler, T. F.
    We present the Dark Energy Camera (DECam) discovery of the optical counterpart of the first binary neutron star merger detected through gravitational-wave emission, GW170817. Our observations commenced 10.5 hr post-merger, as soon as the localization region became accessible from Chile. We imaged 70 deg2 in the i and z bands, covering 93% of the initial integrated localization probability, to a depth necessary to identify likely optical counterparts (e.g., a kilonova). At 11.4 hr post-merger we detected a bright optical transient located 10.”6 from the nucleus of NGC 4993 at redshift z = 0.0098, consistent (for H_0 = 70 km s^(−1)...

  4. Measurement of the inclusive energy spectrum in the very forward direction in proton-proton collisions at √s = 13 TeV

    Sirunyan, A. M.; Anderson, D.; Bendavid, J.; Bornheim, A.; Bunn, J.; Duarte, J.; Lawhorn, J. M.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    The differential cross section for inclusive particle production as a function of energy in proton-proton collisions at a center-of-mass energy of 13 TeV is measured in the very forward region of the CMS detector. The measurement is based on data collected with the CMS apparatus at the LHC, and corresponds to an integrated luminosity of 0.34 μb^(−1). The energy is measured in the CASTOR calorimeter, which covers the pseudorapidity region −6.6 < η < −5.2. The results are given as a function of the total energy deposited in CASTOR, as well as of its electromagnetic and hadronic components. The spectra...

  5. Calibration of Ultraviolet, Mid-infrared, and Radio Star Formation Rate Indicators

    Brown, Michael J. I.; Moustakas, John; Kennicutt, Robert C.; Bonne, Nicolas J.; Intema, Huib T.; de Gasperin, Francesco; Boquien, Médéric; Jarrett, T. H.; Cluver, Michelle E.; Smith, J.-D. T.; da Cunha, Elisabete; Imanishi, Masatoshi; Armus, Lee; Brandl, Bernhard R.; Peek, J. E. G.
    We present calibrations for star formation rate (SFR) indicators in the ultraviolet, mid-infrared, and radio-continuum bands, including one of the first direct calibrations of 150 MHz as an SFR indicator. Our calibrations utilize 66 nearby star-forming galaxies with Balmer-decrement-corrected luminosities, which span five orders of magnitude in SFR and have absolute magnitudes of -24 < M_r < -12. Most of our photometry and spectrophotometry are measured from the same region of each galaxy, and our spectrophotometry has been validated with SDSS photometry, so our random and systematic errors are small relative to the intrinsic scatter seen in SFR indicator calibrations....

  6. In Vitro Corrosion Properties of Mg Matrix In Situ Composites Fabricated by Spark Plasma Sintering

    Cao, Nguyen Q.; Pham, Dinh N.; Kai, Narita; Dinh, Hai V.; Hiromoto, Sachiko; Kobayashi, Equo
    Mg matrix in situ composites were fabricated from Mg and ZnO powder by a spark plasma sintering method. The composition and microstructure of the sintered samples were characterized. Corrosion properties of fabricated composites were evaluated by immersion and by electrochemical tests using Hanks’ solution. The results showed that the formation of in situ products improved significantly the corrosion resistance of the fabricated composites compared with pure Mg; Mg-10 wt % ZnO composites especially exhibited the lowest corrosion rate. In addition, an energy-dispersive X-ray (EDX) analysis showed that calcium phosphate formed as a corrosion product on the surface of Mg-10 wt...

  7. Electrochemistry in ionic liquids: Case study of a manganese corrole

    McNicholas, Brendon J.; Blumenfeld, Carl; Kramer, Wesley W.; Grubbs, Robert H.; Winkler, Jay R.; Gray, Harry B.
    Voltammetry of [5,10,15-tris(pentafluorophenylcorrole)]Mn(III) was investigated in four different ionic liquids (ILs): 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm-TFSI); 1-ethyl-3-methylimidazolium ethylsulfate (EMIm-EtOSO_3); 1-ethyl-3-methylimidazolium triflate (EMIm-OTf); and 1-ethyl-3-methylimidazolium tetracyanoborate (EMIm-TCB). We found that Mn^(IV/III) E_(1/2) values depend on IL counter anion: OTf–< EtOSO_3− < TFSI− < TCB−. In EMIm-TCB and BMIm- TFSI, reversible, diffusion-controlled MnIV/III reactions occurred, as evidenced in each case by the ratio of anodic to cathodic diffusion coefficients over a range of scan rates. Axial coordination was evidenced by a cathodic to anodic diffusion coefficient ratio greater than one, an increasing cathodic to anodic peak current ratio with increasing scan rate, and a...

  8. Echinobase: an expanding resource for echinoderm genomic information

    Kudtarkar, Parul; Cameron, R. Andrew
    Echinobase, a web accessible information system of diverse genomics and biological data for the echinoderm clade, grew out of SpBase, the first echinoderm genome project for sea urchin, Strongylocentrotus purpuratus. Sea urchins and their relatives are utilitarian research models in fields ranging from marine biology to developmental biology and gene regulatory systems. Echinobase is a user-friendly web interface that links an array of biological data that would otherwise have been tedious and frustrating for researchers to extract and organize. The system hosts a powerful gene search engine, genomics browser and other bioinformatics tools to investigate genomics and high throughput data....

  9. High-frequency wavepackets in turbulent jets

    Sasaki, Kenzo; Cavalieri, André V. G.; Jordan, Peter; Schmidt, Oliver T.; Colonius, Tim; Brès, Guillaume A.
    Wavepackets obtained as solutions of the flow equations linearised around the mean flow have been shown in recent work to yield good agreement, in terms of amplitude and phase, with those educed from turbulent jets. Compelling agreement has been demonstrated, for the axisymmetric and first helical mode, up to Strouhal numbers close to unity. We here extend the range of validity of wavepacket models to Strouhal number St = 4.0 and azimuthal wavenumber m = 4 by comparing solutions of the parabolised stability equations with a well-validated large-eddy simulation of a Mach 0.9 turbulent jet. The results show that the...

  10. Best practices for managing large CryoEM facilities

    Alewijnse, Bart; Chen, Songye
    This paper provides an overview of the discussion and presentations from the Workshop on the Management of Large CryoEM Facilities held at the New York Structural Biology Center, New York, NY on February 6–7, 2017. A major objective of the workshop was to discuss best practices for managing cryoEM facilities. The discussions were largely focused on supporting single-particle methods for cryoEM and topics included: user access, assessing projects, workflow, sample handling, microscopy, data management and processing, and user training.

  11. Minimal Influence of [NiFe] Hydrogenase on Hydrogen Isotope Fractionation in H_2-Oxidizing Cupriavidus necator

    Campbell, Brian J.; Sessions, Alex L.; Fox, Daniel N.; Paul, Blair G.; Qin, Qianhui; Kellermann, Matthias Y.; Valentine, David L.
    Fatty acids produced by H_2-metabolizing bacteria are sometimes observed to be more D-depleted than those of photoautotrophic organisms, a trait that has been suggested as diagnostic for chemoautotrophic bacteria. The biochemical reasons for such a depletion are not known, but are often assumed to involve the strong D-depletion of H_2. Here, we cultivated the bacterium Cupriavidus necator H16 (formerly Ralstonia eutropha H16) under aerobic, H_2-consuming, chemoautotrophic conditions and measured the isotopic compositions of its fatty acids. In parallel with the wild type, two mutants of this strain, each lacking one of two key hydrogenase enzymes, were also grown and measured....

  12. Change in the magnitude and mechanisms of global temperature variability with warming

    Brown, Patrick T.; Ming, Yi; Li, Wenhong; Hill, Spencer A.
    Natural unforced variability in global mean surface air temperature (GMST) can mask or exaggerate human-caused global warming, and thus a complete understanding of this variability is highly desirable. Significant progress has been made in elucidating the magnitude and physical origins of present-day unforced GMST variability, but it has remained unclear how such variability may change as the climate warms. Here we present modelling evidence that indicates that the magnitude of low-frequency GMST variability is likely to decline in a warmer climate and that its generating mechanisms may be fundamentally altered. In particular, a warmer climate results in lower albedo at...

  13. An M_w = 7.7 slow earthquake in 1960 near the Aysén Fjord region, Chile

    Kanamori, Hiroo; Rivera, Luis
    We re-examine the source characteristics of an M_s = 6.9 earthquake in Chile which occurred on 1960 June 6, near the Aysén Fjord region where a remarkable earthquake swarm occurred in 2007 with more than 7000 earthquakes and hundreds of landslides. The June 6 event occurred during the aftershock activity of the 1960 May 22, M_w = 9.5 great Chilean earthquake. A recently found well-calibrated strain seismogram of the June 6 event recorded at Isabella (ISA), California, is the impetus to this study. We confirm that this event is a slow earthquake caused by a source process extending at least...

  14. Forest Conservation in the Anthropocene: Science, Policy, and Practice [Book Review]

    Pluymers, Keith
    Earth, according to some researchers, has entered a new phase in which human activity is the dominant influence over planetary systems—the Anthropocene. Uncertainty remains about when it began, what unit of geologic time it comprises, and whether the proposed periodization will pass the International Commission on Stratigraphy. Nonetheless, the term has become popular in a wide range of academic disciplines and in popular writing. Forest Conservation in the Anthropocene, a valuable collection of essays from forestry officials, ecologists, and policy scholars, works with the term at its broadest level. Forestry in the Anthropocene requires adaptive responses to anthropogenic climate change...

  15. Imbricated slip rate processes during slow slip transients imaged by low-frequency earthquakes

    Lengliné, O.; Frank, W. B.; Marsan, D.; Ampuero, J.-P.
    Low Frequency Earthquakes (LFEs) often occur in conjunction with transient strain episodes, or Slow Slip Events (SSEs), in subduction zones. Their focal mechanism and location consistent with shear failure on the plate interface argue for a model where LFEs are discrete dynamic ruptures in an otherwise slowly slipping interface. SSEs are mostly observed by surface geodetic instruments with limited resolution and it is likely that only the largest ones are detected. The time synchronization of LFEs and SSEs suggests that we could use the recorded LFEs to constrain the evolution of SSEs, and notably of the geodetically-undetected small ones. However,...

  16. A model of smoldering combustion applied to flexible polyurethane foams

    Ohlemiller, T. J.; Bellan, J.; Rogers, F.
    Smoldering combustion, particularly in upholstery and bedding materials, has been proven a serious life hazard. The simplest representation of this hazard situation is one-dimensional downward propagation of a smolder wave against a buoyant upflow (cocurrent smolder); the configuration treated here is identical in all respects to this except for the presence of a forced flow replacing the buoyant one. The complex degradation chemistry of the polyurethanes is here reduced to the two major overall reactions of char formation and char oxidation. The model solutions, which are in reasonable agreement with experimental results, show the smolder process to be oxygen-limited, which...

  17. High-Pressure Binary Mass Diffusion Coefficients for Combustion Applications

    Harstad, Kenneth; Bellan, Josette
    A scaling for binary mass diffusion coefficients is developed using a corresponding states expression based on kinetic theory. The scaling is used to form nondimensional diffusion coefficients. Available data for high-pressure binary mass diffusion coefficients related to combustion applications are processed in conjunction with the scaling, leading to recommended scaled coefficient fits as a function of the reduced density. Data uncertainties and possible interpretation difficulties are examined. A means for comprehensive diffusion coefficient modeling over a broad (3 orders of magnitude) pressure range is suggested.

  18. The Orbiting Carbon Observatory (OCO-2) tracks 2–3 peta-gram increase in carbon release to the atmosphere during the 2014–2016 El Niño

    Patra, Prabir K.; Crisp, David; Kaiser, Johannes W.; Wunch, Debra; Saeki, Tazu; Ichii, Kazuhito; Sekiya, Takashi; Wennberg, Paul O.; Feist, Dietrich G.; Pollard, David F.; Griffith, David W. T.; Velazco, Voltaire A.; De Mazière, M.; Sha, Mahesh K.; Roehl, Coleen; Chatterjee, Abhishek; Ishijima, Kentaro
    The powerful El Niño event of 2015–2016 – the third most intense since the 1950s – has exerted a large impact on the Earth’s natural climate system. The column-averaged CO_2 dry-air mole fraction (XCO_2) observations from satellites and ground-based networks are analyzed together with in situ observations for the period of September 2014 to October 2016. From the differences between satellite (OCO-2) observations and simulations using an atmospheric chemistry-transport model, we estimate that, relative to the mean annual fluxes for 2014, the most recent El Niño has contributed to an excess CO_2 emission from the Earth’s surface (land + ocean) to the...

  19. A priori subgrid analysis of temporal mixing layers with evaporating droplets

    Okong’o, Nora; Bellan, Josette
    Subgrid analysis of a transitional temporal mixing layer with evaporating droplets has been performed using three sets of results from a direct numerical simulation (DNS) database, with Reynolds numbers (based on initial vorticity thickness) as large as 600 and with droplet mass loadings as large as 0.5. In the DNS, the gas phase is computed using an Eulerian formulation, with Lagrangian droplet tracking. The large eddy simulation (LES) equations corresponding to the DNS are first derived, and key assumptions in deriving them are first confirmed by using the DNS database. Since LES of this flow requires the computation of droplet...

  20. Shielding Theory of Enclosures with Apertures

    Mendez, Horacio Augusto
    Present methods for computing the shielding efficiency of metallic plates with apertures are based on the analysis of a plane wave incident on an infinite conducting sheet. When applied to actual enclosures with internal radiation sources, these methods lose all validity, and obviously fail to predict the measured results. Semi-empirical formulas are available for special cases, but no serious analytic investigation has ever been conducted. This dissertation develops the theory of electromaqnetic radiation from metallic enclosures with apertures, excited by an internal source at frequencies below the fundamental resonance of the enclosure. The enclosure with an aperture is analyzed from two different...

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