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rss_1.0 Recursos de colección

Caltech Authors (90,284 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 39,718

1. Quasi Two-Dimensional Flows Through a Cascade - Mani, R.; Acosta, A. J.
A thin airfoil theory is developed for airfoils spanning a slowly diverging or converging channel, the motivation being to predict, theoretically, the effect of varying axial velocity on the cascade performance of axial flow compressor rows.

2. Production of Accelerated Cavitation Damage by an Acoustic Field in a Cylindrical Cavity - Ellis, A. T.
A convenient and economical method for the production of cavitation damage is described. Cavitation is generated in the region of the maximum pressure amplitude of an acoustic field in a resonant cylindrical container. The specimen surface to be damaged is a stationary boundary in the system and is therefore not subject to accelerations such as occur in conventional magnetostriction devices for cavitation damage study. The absence of these accelerations eliminates any possibility of premature material removal from cavitation weakened surfaces. Mathematical analysis of the dynamics of cavitation should also be facilitated. It is shown that simple assumptions lead to an...

3. Pressure Distributions on the Vanes of a Radial Flow Impeller - Morelli, D. A.
Theoretical approaches give very little guide to the design of radial arrays of vanes for the addition of energy to a fluid. The usual approach of the designer has been to design inlet and outlet angles according to the theory for an infinite number of vanes, and to connect these two angles by some plausible curve. Modifications are introduced according to the experience and records of the designer. The final justification of the design by measurements of the differential pressure is very rarely made. The present paper reports the first of a series of planned experiments to develop necessary background knowledge. An...

4. From neuronal populations to behavior: a computational journey - Graf, Arnulf B. A.
Cognitive behaviors originate in the responses of neuronal populations. We have a reasonable understanding of how the activity of a single neuron can be related to a specific behavior. However, it is still unclear how more complex behaviors are inferred from the responses of neuronal populations. This is a particularly timely problem because multi-neuronal recording techniques have recently become increasingly available, simultaneously spurring advances in the analysis of neuronal population data. These developments are, however, constrained by the challenges of combining theoretical and experimental approaches because both approaches have their unique set of constraints. A solution to this problem is...

5. Herschel SPIRE FTS relative spectral response calibration - Fulton, Trevor; Hopwood, Rosalind; Baluteau, Jean-Paul; Benielli, Dominique; Imhof, Peter; Lim, Tanya; Lu, Nanyao; Marchili, Nicola; Naylor, David; Polehampton, Edward T.; Swinyard, Bruce; Valtchanov, Ivan
Herschel/SPIRE Fourier transform spectrometer (FTS) observations contain emission from both the Herschel Telescope and the SPIRE Instrument itself, both of which are typically orders of magnitude greater than the emission from the astronomical source, and must be removed in order to recover the source spectrum. The effects of the Herschel Telescope and the SPIRE Instrument are removed during data reduction using relative spectral response calibration curves and emission models. We present the evolution of the methods used to derive the relative spectral response calibration curves for the SPIRE FTS. The relationship between the calibration curves and the ultimate sensitivity of...

6. BC4GO: a full-text corpus for the BioCreative IV GO task - Van Auken, Kimberly; Schaeffer, Mary L.; McQuilton, Peter; Laulederkind, Stanley J. F.; Li, Donghui; Wang, Shur-Jen; Hayman, G. Thomas; Tweedie, Susan; Arighi, Cecilia N.; Done, James; Müller, Hans-Michael; Sternberg, Paul W.; Mao, Yuqing; Wei, Chih-Hsuan; Lu, Zhiyong
Gene function curation via Gene Ontology (GO) annotation is a common task among Model Organism Database groups. Owing to its manual nature, this task is considered one of the bottlenecks in literature curation. There have been many previous attempts at automatic identification of GO terms and supporting information from full text. However, few systems have delivered an accuracy that is comparable with humans. One recognized challenge in developing such systems is the lack of marked sentence-level evidence text that provides the basis for making GO annotations. We aim to create a corpus that includes the GO evidence text along with...

7. The Rest-frame Ultraviolet Structure of 0.5 < z < 1.5 Galaxies - Bond, Nicholas A.; Gardner, Jonathan P.; de Mello, Duilia F.; Teplitz, Harry I.; Rafelski, Marc; Koekemoer, Anton M.; Coe, Dan; Grogin, Norman; Gawiser, Eric; Ravindranath, Swara; Scarlata, Claudia
We present the rest-frame UV wavelength dependence of the Petrosian-like half-light radius (r_(50)), and the concentration parameter for a sample of 198 star-forming galaxies at 0.5 < z < 1.5. We find a ~5% decrease in r_(50) from 1500 Å to 3000 Å, with half-light radii at 3000 Å ranging from 0.6 kpc to 6 kpc. We also find a decrease in concentration of ~0.07 (1.9 < C_(3000) < 3.9). The lack of a strong relationship between r_(50) and wavelength is consistent with a model in which clumpy star formation is distributed over length scales comparable to the galaxy's rest-frame...

8. Initial Results from NuSTAR Observations of the Norma Arm - Bodaghee, Arash; Tomsick, John A.; Krivonos, Roman; Stern, Daniel; Bauer, Franz E.; Fornasini, Francesca M.; Barrière, Nicolas M.; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Gotthelf, Eric V.; Hailey, Charles J.; Harrison, Fiona A.; Hong, Jaesub; Mori, Kaya; Zhang, William W.
Results are presented for an initial survey of the Norma Arm gathered with the focusing hard X-Ray Telescope NuSTAR. The survey covers 0.2 deg^2 of sky area in the 3-79 keV range with a minimum and maximum raw depth of 15 ks and 135 ks, respectively. Besides a bright black-hole X-ray binary in outburst (4U 1630–47) and a new X-ray transient (NuSTAR J163433–473841), NuSTAR locates three sources from the Chandra survey of this region whose spectra are extended above 10 keV for the first time: CXOU J163329.5–473332, CXOU J163350.9–474638, and CXOU J163355.1–473804. Imaging, timing, and spectral data from a broad...

9. The Radius Distribution of Planets around Cool Stars - Morton, Timothy D.; Swift, Jonathan
We calculate an empirical, non-parametric estimate of the shape of the period-marginalized radius distribution of planets with periods less than 150 days using the small yet well-characterized sample of cool (T_(eff) < 4000 K) dwarf stars in the Kepler catalog. In particular, we present and validate a new procedure, based on weighted kernel density estimation, to reconstruct the shape of the planet radius function down to radii smaller than the completeness limit of the survey at the longest periods. Under the assumption that the period distribution of planets does not change dramatically with planet radius, we show that the occurrence...

10. Medusa: A Novel Gene Drive System for Confined Suppression of Insect Populations - Marshall, John M.; Hay, Bruce A.
Gene drive systems provide novel opportunities for insect population suppression by driving genes that confer a fitness cost into pest or disease vector populations; however regulatory issues arise when genes are capable of spreading across international borders. Gene drive systems displaying threshold properties provide a solution since they can be confined to local populations and eliminated through dilution with wild-types. We propose a novel, threshold-dependent gene drive system, Medusa, capable of inducing a local and reversible population crash. Medusa consists of four components - two on the X chromosome, and two on the Y chromosome. A maternally-expressed, X-linked toxin and...

11. Lewis Acid Promoted Titanium Alkylidene Formation: Off-Cycle Intermediates Relevant to Olefin Trimerization Catalysis - Sattler, Aaron; VanderVelde, David G.; Labinger, Jay A.; Bercaw, John E.
Two new precatalysts for ethylene and α-olefin trimerization, (FI)Ti(CH_2SiMe_3)_2Me and (FI)Ti(CH_2CMe_3)_2Me (FI = phenoxy-imine), have been synthesized and structurally characterized by X-ray diffraction. (FI)Ti(CH_2SiMe_3)_2Me can be activated with 1 equiv of B(C_6F_5)_3 at room temperature to give the solvent-separated ion pair [(FI)Ti(CH_2SiMe_3)_2][MeB(C_6F_5)_3], which catalytically trimerizes ethylene or 1-pentene to produce 1-hexene or C_(15) olefins, respectively. The neopentyl analogue (FI)Ti(CH_2CMe_3)_2Me is unstable toward activation with B(C_6F_5)_3 at room temperature, giving no discernible diamagnetic titanium complexes, but at −30 °C the following can be observed by NMR spectroscopy: (i) formation of the bis-neopentyl cation [(FI)Ti(CH_2CMe_3)_2]^+, (ii) α-elimination of neopentane to give the...

12. Substrate Dependent Water Splitting with Ultrathin α‑Fe_2O_3 Electrodes - Zandi, Omid; Beardslee, Joseph A.; Hamann, Thomas
Thin films of hematite (α-Fe_2O_3) were deposited by atomic layer deposition (ALD), and the effects of metal oxide underlayers on the photocatalytic water oxidation performance were investigated. It was found that a Ga_2O_3 underlayer dramatically enhances the water oxidation performance of the thinnest hematite films. The performance enhancement is attributed to the increased crystallinity of the ultrathin films induced by the oxide underlayers. The degree of crystallinity was examined by Raman line shape analysis of the characteristic hematite phonon modes. It was found that multiple metal oxide underlayers, including Nb_2O_5, ITO, and WO_3, increase the film crystallinity compared to hematite...

13. Nonresponse and Mode Effects in Self- and Interviewer-Administered Surveys - Atkeson, Lonna Rae; Adams, Alex N.; Alvarez, R. Michael
We examine the quality of two probability-based polls, one interviewer administered (telephone) and one self-administered (Internet and mail mixed mode survey). The polls use the same sampling frame (registered voters) and the same questions. First, we examine the representativeness of both surveys using information known about the population, and although we find important differences between the two in terms of sampling and nonresponse bias, we also find that both surveys represent the underlying population despite low response rates. We also test for mode effects between surveys due to social desirability and how it influences nondifferentiation or satisficing. Using a variety...

14. GRB 051008: a long, spectrally hard dust-obscured GRB in a Lyman-break galaxy at z ≈ 2.8 - Volnova, A. A.; Pozanenko, A. S.; Gorosabel, J.; Perley, D. A.; Frederiks, D. D.; Kann, D. A.; Rumyantsev, V. V.; Biryukov, V. V.; Burkhonov, O.; Castro-Tirado, A. J.; Ferrero, P.; Golenetskii, S. V.; Klose, S.; Loznikov, V. M.; Minaev, P. Yu; Stecklum, B.; Svinkin, D. S; Tsvetkova, A. E.; de Ugarte Postigo, A.; Ulanov, M. V.
We present observations of the dark gamma-ray burst GRB 051008 provided by Swift/BAT, Swift/XRT, Konus-WIND, INTEGRAL/SPI-ACS in the high-energy domain and the Shajn, Swift/UVOT, Tautenburg, NOT, Gemini and Keck I telescopes in the optical and near-infrared bands. The burst was detected only in gamma- and X-rays and neither a prompt optical nor a radio afterglow was detected down to deep limits. We identified the host galaxy of the burst, which is a typical Lyman-break galaxy (LBG) with R-magnitude of 24.06 ± 0.10 mag. A redshift of the galaxy of z=2.77^(+0.15)_(−0.20) is measured photometrically due to the presence of a clear,...

15. Solid-State Characterization and Photoinduced Intramolecular Electron Transfer in a Nanoconfined Octacationic Homo[2]Catenane - Barnes, Jonathan C.; Frasconi, Marco; Young, Ryan M.; Khdary, Nezar H.; Liu, Wei-Guang; Dyar, Scott M.; McGonigal, Paul R.; Gibbs-Hall, Ian C.; Diercks, Christian S.; Sarjeant, Amy A.; Stern, Charlotte L.; Goddard, William A., III; Wasielewski, Michael R.; Stoddart, J. Fraser
An octacationic homo[2]catenane comprised of two mechanically interlocked cyclobis(paraquat-p-phenylene) rings has been obtained from the oxidation of the septacationic monoradical with nitrosonium hexafluoroantimonate. The nanoconfinement of normally repulsive bipyridinium units results in the enforced π-overlap of eight positively charged pyridinium rings in a volume of <1.25 nm^3. In the solid state, the torsional angles around the C–C bonds between the four pairs of pyridinium rings range between 16 and 30°, while the π–π stacking distances between the bipyridinium units are extended for the inside pair and contracted for the pairs on the outside—a consequence of Coulombic repulsion between the inner...

16. The RoboPol optical polarization survey of gamma-ray-loud blazars - Pavlidou, V.; King, O. G.; Hovatta, T.; Baloković, M.; Pearson, T. J.; Readhead, A. C. S.
We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during the 2013 May–June commissioning of the instrument, constitute a single-epoch linear polarization survey of a sample of gamma-ray-loud blazars, defined according to unbiased and objective selection criteria, easily reproducible in simulations, as well as a comparison sample of, otherwise similar, gamma-ray-quiet blazars. As such, the results of this survey are appropriate for both phenomenological population studies and for tests of theoretical population models. We have measured polarization fractions as low as 0.015 down to R-mag of 17 and as...

17. The RoboPol pipeline and control system - King, O. G.; Baloković, M.; Hovatta, T.; Pearson, T. J.; Readhead, A. C. S.
We describe the data reduction pipeline and control system for the RoboPol project. The RoboPol project is monitoring the optical R-band magnitude and linear polarization of a large sample of active galactic nuclei that is dominated by blazars. The pipeline calibrates and reduces each exposure frame, producing a measurement of the magnitude and linear polarization of every source in the 13 arcmin × 13 arcmin field of view. The control system combines a dynamic scheduler, real-time data reduction, and telescope automation to allow high-efficiency unassisted observations.

18. Near-infrared counterparts of ultraluminous X-ray sources - Heida, M.; Jonker, P. G.; Torres, M. A. P.; Kool, E.; Servillat, M.; Roberts, T. P.; Groot, P. J.; Walton, D. J.; Moon, D.-S.; Harrison, F. A.
In this paper, we present the results of the first systematic search for counterparts to nearby ultraluminous X-ray sources (ULXs) in the near-infrared (NIR). We observed 62 ULXs in 37 galaxies within 10 Mpc and discovered 17 candidate NIR counterparts. The detection of 17 out of 62 ULX candidates points to intrinsic differences between systems that show and those that do not show infrared emission. For six counterparts, we conclude from the absolute magnitudes and – in some cases – additional information such as morphology and previously reported photometric or spectroscopic observations, that they are likely background active galactic nuclei...

19. Molecular gas properties of UV-bright star-forming galaxies at low redshift - Gonçalves, Thiago S.; Basu-Zych, Antara; Overzier, Roderik A.; Pérez, Laura; Martin, D. Christopher
Lyman break analogues (LBAs) are a population of star-forming galaxies at low redshift (z ∼ 0.2) selected in the ultraviolet (UV). These objects present higher star formation rates and lower dust extinction than other galaxies with similar masses and luminosities in the local universe. In this work, we present results from a survey with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) array to detect CO(1–0) emission in LBAs, in order to analyse the properties of the molecular gas in these galaxies. Our results show that LBAs follow the same Schmidt–Kennicutt law as local galaxies. On the other hand,...

20. Automated algorithms to identify and locate grains of specific composition for NIR hyperspectral microscopes: Application to the MicrOmega instrument onboard ExoMars - Pilorget, C.; Bibring, J.-P.
MicrOmega is an NIR hyperspectral microscope that has been selected as part of the ExoMars rover payload. We demonstrate here that this instrument has the capability through automated algorithms to identify and locate grains of interest (composition-wise) within a collected sample that could be further targeted by other instruments within the ExoMars payload. Results will also be used to perform an optimized compression of the data, with regard to the relevance of the different grains, in order to limit the volume of downloaded data. The algorithms that we have developed, using combined spectral criteria and different tests to avoid false...

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