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Caltech Authors (108,052 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 47,360

1. The Infrared Imaging Spectrograph (IRIS) for TMT: Volume Phase Holographic Grating Performance Testing and Discussion - Chen, Shaojie; Meyer, Elliot; Wright, Shelley A.; Moore, Anna M.; Larkin, James E.; Maire, Jérôme; Mieda, Etsuko; Simard, Luc
Maximizing the grating efficiency is a key goal for the first light instrument IRIS (Infrared Imaging Spectrograph) currently being designed to sample the diffraction limit of the TMT (Thirty Meter Telescope). Volume Phase Holographic (VPH) gratings have been shown to offer extremely high efficiencies that approach 100% for high line frequencies (i.e., 600 to 6000l/mm), which has been applicable for astronomical optical spectrographs. However, VPH gratings have been less exploited in the near-infrared, particularly for gratings that have lower line frequencies. Given their potential to offer high throughputs and low scattered light, VPH gratings are being explored for IRIS as...

2. Quantum yield of chlorine-atom formation in the photodissociation of chlorine peroxide (ClOOCl) at 308 nm - Molina, M. J.; Colussi, A. J.; Molina, L. T.; Schindler, R. N.; Tso, T.-L.
The production of Cl atoms in the laser flash photolysis of ClOOCl at 308 nm has been investigated by time-resolved atomic resonance fluorescence at 235 K. A value of φ = 1.03 ± 0.12 has been obtained for the primary quantum yield based on an absorption cross section ratio σ_(245)/σ_(308) = 22 for ClOOCl at 245 and 308 nm.

3. Iris: An extensible application for building and analyzing spectral energy distributions - Laurino, O.; Budynkiewicz, J.; D’Abrusco, R.; Bonaventura, N.; Busko, I.; Cresitello-Dittmar, M.; Doe, S. M.; Ebert, R.; Evans, J. D.; Norris, P.; Pevunova, O.; Refsdal, B.; Thomas, B.; Thompson, R.
Iris is an extensible application that provides astronomers with a user-friendly interface capable of ingesting broad-band data from many different sources in order to build, explore, and model spectral energy distributions (SEDs). Iris takes advantage of the standards defined by the International Virtual Observatory Alliance, but hides the technicalities of such standards by implementing different layers of abstraction on top of them. Such intermediate layers provide hooks that users and developers can exploit in order to extend the capabilities provided by Iris. For instance, custom Python models can be combined in arbitrary ways with the Iris built-in models or with...

4. Non-parametric stochastic subset optimization for design problems with reliability constraints - Jia, G.; Taflanidis, A. A.; Beck, J. L.
The Non-Parametric Stochastic Subset Optimization (NP-SSO) is a recently developed algorithm appropriate for optimization problems that use the system reliability as objective function and involve computationally expensive numerical models. This paper discusses its extension to reliability-based design optimization (RBDO) applications involving the system reliability as a design constraint. The foundation of NP-SSO is the formulation of an augmented problem where the design variables are artificially considered as uncertain. In this context, the system reliability is proportional to an auxiliary probability density function related to the design variables. NP-SSO is based on simulation of samples from this density and approximates the system reliability through kernel density estimation...

5. Effect of NiO sintering-aid on hydration kinetics and defect-chemical parameters of BaZr_(0.8)Y_(0.2)O_(3 – Δ) - Kim, E.; Yamazaki, Y.; Haile, S. M.; Yoo, H.-I.
The influence of NiO, used as a sintering aid, on the transport properties of BaZr_(0.8)Y_(0.2)O_(3 – Δ) was investigated by monitoring electrical conductivity relaxation of specimens with and without NiO during hydration in atmospheres of different oxygen activities at 700 and 800 °C. The chemical diffusivities of H and O governing the kinetics were precisely evaluated from the transient conductivity, and all the defect-chemical parameters — the two external equilibrium constants and mobilities of all the carriers, VO· ·, Hi· and h· — were determined from the steady-state equilibrium conductivity. It is found that the processing benefits afforded by NiO...

6. The Effect of Detergent, Temperature, and Lipid on the Oligomeric State of MscL Constructs: Insights from Mass Spectrometry - Reading, Eamonn; Walton, Troy A.; Liko, Idlir; Marty, Michael T.; Laganowsky, Arthur; Rees, Douglas C.; Robinson, Carol V.
The mechanosensitive channel of large conductance (MscL) acts as an emergency release valve for osmotic shock of bacteria preventing cell lysis. The large pore size, essential for function, requires the formation of oligomers with tetramers, pentamers, or hexamers observed depending on the species and experimental approach. We applied non-denaturing (native) mass spectrometry to five different homologs of MscL to determine the oligomeric state under more than 50 different experimental conditions elucidating lipid binding and subunit stoichiometry. We found equilibrium between pentameric and tetrameric species, which can be altered by detergent, disrupted by binding specific lipids, and perturbed by increasing temperature...

7. Enhancement of the Spitzer Infrared Array Camera Distortion Correction for Parallax Measurements - Lowrance, Patrick J.; Carey, Sean J.; Ingalls, James G.; Surace, Jason; Capak, Peter; Stauffer, John; Beichman, Chas; Shupe, David; Kirkpatrick, J. Davy
The Spitzer Space Telescope Infrared Array (IRAC) offers a rare opportunity to measure distances and determine physical properties of the faintest and coldest brown dwarfs. The current distortion correction is a 3rd order polynomial represented by TAN-SIP parameters within the headers. The current correction, good to 100 mas, was derived from deep imaging, using marginally resolved galaxies in some cases, and has remained stable throughout both the cryogenic and warm mission. Using recent Spitzer calibration observations mapped to HST/ACS calibration observations of 47 Tuc with an absolute accuracy good to 1 mas, we are working towards a possible 5th order...

8. Laboratory evolution of peroxide-mediated cytochrome P450 hydroxylation - Joo, Hyun; Lin, Zhanglin; Arnold, Frances H.; Aust, Steven D.
The article entitled Laboratory evolution of peroxidemediated cytochrome P450 hydroxylations, by Hyun Joo, Zhanglin Lin and Francis H. Arnold of the Division of Chemistry and Chemical Engineering, California Institute of Technology, recently communicated in Nature, is an excellent example of the revolution in the biological sciences. We frequently hear that we are in the midst of an informational revolution. If one simply considers the fact that all biological information exists in DNA, it is possible to envision the biological informational revolution. Alternatively, the term technological revolution is applied to the many recent advances in several fields, including the biological sciences. Both the informational and technological revolution can be readily recognized in the article by...

9. Investigating Hα, UV, and IR Star-formation Rate Diagnostics for a Large Sample of z ~ 2 Galaxies - Shivaei, Irene; Reddy, Naveen A.; Steidel, Charles C.; Shapley, Alice E.
We use a sample of 262 spectroscopically confirmed star-forming galaxies at redshifts 2.08 ≤ z ≤ 2.51 to compare Hα, ultraviolet (UV), and IR star formation rate (SFR) diagnostics and to investigate the dust properties of the galaxies. At these redshifts, the Hα line shifts to the K_s band. By comparing K_s-band photometry to underlying stellar population model fits to other UV, optical, and near-infrared data, we infer the Hα flux for each galaxy. We obtain the best agreement between Hα- and UV-based SFRs if we assume that the ionized gas and stellar continuum are reddened by the same value...

10. Studying Extragalactic Background Fluctuations with the Cosmic Infrared Background ExpeRiment 2 (CIBER-2) - Lanz, Alicia; Arai, Toshiaki; Battle, John; Bock, James; Cooray, Asantha; Hristov, Viktor; Korngut, Phillip; Lee, Dae Hee; Mason, Peter; Matsumoto, Toshio; Matsuura, Shuji; Morford, Tracy; Onishi, Yosuke; Shirahata, Mai; Tsumura, Kohji; Wada, Takehiko; Zemcov, Michael
Fluctuations in the extragalactic background light trace emission from the history of galaxy formation, including the emission from the earliest sources from the epoch of reionization. A number of recent near-infrared measure- ments show excess spatial power at large angular scales inconsistent with models of z < 5 emission from galaxies. These measurements have been interpreted as arising from either redshifted stellar and quasar emission from the epoch of reionization, or the combined intra-halo light from stars thrown out of galaxies during merging activity at lower redshifts. Though astrophysically distinct, both interpretations arise from faint, low surface brightness source populations...

11. Using drift scans to improve astrometry with Spitzer - Ingalls, James G.; Carey, Sean J.; Lowrance, Patrick J.; Grillmair, Carl J.; Stauffer, John R.
The Spitzer Space Telescope Infrared Array Camera (IRAC) is the only space-based instrument currently capable of continuous long duration monitoring of brown dwarfs to detect variability and characterize their atmospheres. Any such studies are limited, however, by the accuracy to which we know the positions and distances to these targets (most of which are newly discovered and therefore do not yet have multiple epochs of astrometric data). To that end, we have begun a new initiative to adapt the astrometric drift scanning technique employed by the Hubble Space Telescope to enhance Spitzer measurements of parallaxes and proper motions of brown...

12. Random normal matrices and Ward identities - Ameur, Yacin; Hedenmalm, Haakan; Makarov, Nikolai
We consider the random normal matrix ensemble associated with a potential in the plane of sufficient growth near infinity. It is known that asymptotically as the order of the random matrix increases indefinitely, the eigenvalues approach a certain equilibrium density, given in terms of Frostman’s solution to the minimum energy problem of weighted logarithmic potential theory. At a finer scale, we may consider fluctuations of eigenvalues about the equilibrium. In the present paper, we give the correction to the expectation of the fluctuations, and we show that the potential field of the corrected fluctuations converge on smooth test functions to...

13. Star-forming Blue ETGs in Two Newly Discovered Galaxy Overdensities in the HUDF at z=1.84 and 1.9: Unveiling the Progenitors of Passive ETGs in Cluster Cores - Mei, Simona; Scarlata, Claudia; Pentericci, Laura; Newman, Jeffrey A.; Weiner, Benjamin J.; Ashby, Matthew L. N.; Castellano, Marco; Conselice, Christopher J.; Finkelstein, Steven L.; Galametz, Audrey; Grogin, Norman A.; Koekemoer, Anton M.; Huertas-Company, Marc; Lani, Caterina; Lucas, Ray A.; Papovich, Casey; Rafelski, Marc; Teplitz, Harry I.
We present the discovery of two galaxy overdensities in the Hubble Space Telescope UDF: a proto-cluster, HUDFJ0332.4-2746.6 at z=1.84 ± 0.01, and a group, HUDFJ0332.5-2747.3 at z=1.90 ± 0.01. Assuming viralization, the velocity dispersion of HUDFJ0332.4-2746.6 implies a mass of M_(200) = (2.2 ± 1.8) x 10^(14) M_☉, consistent with the lack of extended X-ray emission. Neither overdensity shows evidence of a red sequence. About $50\%$ of their members show interactions and/or disturbed morphologies, which are signatures of merger remnants or disk instability. Most of their ETGs have blue colors and show recent star formation. These observations reveal for the...

14. Determining the Covering Factor of Compton-thick Active Galactic Nuclei with NuSTAR - Brightman, M.; Baloković, M.; Stern, D.; Arévalo, P.; Ballantyne, D. R.; Bauer, F. E.; Boggs, S. E.; Craig, W. W.; Christensen, F. E.; Comastri, A.; Fuerst, F.; Gandhi, P.; Hailey, C. J.; Harrison, F. A.; Hickox, R. C.; Koss, M.; LaMassa, S.; Puccetti, S.; Rivers, E.; Vasudevan, R.; Walton, D. J.; Zhang, W. W.
The covering factor of Compton-thick (CT) obscuring material associated with the torus in active galactic nuclei (AGNs) is at present best understood through the fraction of sources exhibiting CT absorption along the line of sight (N_H > 1.5 × 10^(24) cm^(−2)) in the X-ray band, which reveals the average covering factor. Determining this CT fraction is difficult, however, due to the extreme obscuration. With its spectral coverage at hard X-rays (>10 keV), Nuclear Spectroscopic Telescope Array (NuSTAR) is sensitive to the AGNs covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a...

15. The Gould's Belt Very Large Array Survey. II. The Serpens Region - Ortiz-Leόn, Gisela N.; Loinard, Laurent; Mioduszewski, Amy J.; Dzib, Sergio A.; Rodríguez, Luis F.; Pech, Gerardo; Rivera, Juana L.; Torres, Rosa M.; Boden, Andrew F.; Hartmann, Lee; Evans, Neal J., II; Briceño, Cesar; Tobin, John J.; Kounkel, Marina A.; González-Lópezlira, Rosa A.
We present deep (~17 μJy) radio continuum observations of the Serpens molecular cloud, the Serpens south cluster, and the W40 region obtained using the Very Large Array in its A configuration. We detect a total of 146 sources, 29 of which are young stellar objects (YSOs), 2 of which are BV stars, and 5 more of which are associated with phenomena related to YSOs. Based on their radio variability and spectral index, we propose that about 16 of the remaining 110 unclassified sources are also YSOs. For approximately 65% of the known YSOs detected here as radio sources, the emission...

16. Understanding the Effects of Stellar Multiplicity on the Derived Planet Radii from Transit Surveys: Implications for Kepler, K2, and TESS - Ciardi, David R.; Beichman, Charles A.; Horch, Elliott P.; Howell, Steve B.
We present a study on the effect of undetected stellar companions on the derived planetary radii for Kepler Objects of Interest (KOIs). The current production of the KOI list assumes that each KOI is a single star. Not accounting for stellar multiplicity statistically biases the planets toward smaller radii. The bias toward smaller radii depends on the properties of the companion stars and whether the planets orbit the primary or the companion stars. Defining a planetary radius correction factor, X_R, we find that if the KOIs are assumed to be single, then, on average, the planetary radii may be underestimated...

17. Dimming and CO absorption toward the AA Tau protoplanetary disk: An infalling flow caused by disk instability? - Zhang, Ke; Crockett, Nathan R.; Salyk, Colette; Pontoppidan, Klaus M.; Turner, Neal J.; Carpenter, John M.; Blake, Geoffrey A.
AA Tau, a classical T Tauri star in the Taurus cloud, has been the subject of intensive photometric monitoring for more than two decades due to its quasi-cyclic variation in optical brightness. Beginning in 2011, AA Tau showed another peculiar variation—its median optical though near-IR flux dimmed significantly, a drop consistent with a 4-mag increase in visual extinction. It has stayed in the faint state since. Here we present 4.7 μm CO rovibrational spectra of AA Tau over eight epochs, covering an 11 yr time span, that reveal enhanced ^(12)CO and ^(13)CO absorption features in the J_low ≤ 13 transitions...

18. Parameter Estimation for Binary Neutron-star Coalescences with Realistic Noise during the Advanced LIGO Era - Berry, Christopher P. L.; Mandel, Ilya; Middleton, Hannah; Singer, Leo P.; Urban, Alex L.; Vecchio, Alberto; Vitale, Salvatore; Cannon, Kipp; Farr, Ben; Farr, Will M.; Graff, Philip B.; Hanna, Chad; Haster, Carl-Johan; Mohapatra, Satya; Pankow, Chris; Price, Larry R.; Sidery, Trevor; Veitch, John
Advanced ground-based gravitational-wave (GW) detectors begin operation imminently. Their intended goal is not only to make the first direct detection of GWs, but also to make inferences about the source systems. Binary neutron-star mergers are among the most promising sources. We investigate the performance of the parameter-estimation (PE) pipeline that will be used during the first observing run of the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) in 2015: we concentrate on the ability to reconstruct the source location on the sky, but also consider the ability to measure masses and the distance. Accurate, rapid sky localization is necessary to alert...

19. The Ferrous Iron-Responsive BqsRS Two-Component System Activates Genes That Promote Cationic Stress Tolerance - Kreamer, Naomi N.; Costa, Flavia; Newman, Dianne K.
The physiological resistance of pathogens to antimicrobial treatment is a severe problem in the context of chronic infections. For example, the mucus-filled lungs of cystic fibrosis (CF) patients are readily colonized by diverse antibiotic-resistant microorganisms, including Pseudomonas aeruginosa. Previously, we showed that bioavailable ferrous iron [Fe(II)] is present in CF sputum at all stages of infection and constitutes a significant portion of the iron pool at advanced stages of lung function decline [R. C. Hunter et al., mBio 4(4):e00557-13, 2013]. P. aeruginosa, a dominant CF pathogen, senses Fe(II) using a two-component signal transduction system, BqsRS, which is transcriptionally active in...

20. Influence of particle-phase state on the hygroscopic behavior of mixed organic-inorganic aerosols - Hodas, N.; Zuend, A.; Mui, W.; Flagan, R. C.; Seinfeld, J. H.
Recent work has demonstrated that organic and mixed organic–inorganic particles can exhibit multiple phase states depending on their chemical composition and on ambient conditions such as relative humidity (RH). To explore the extent to which water uptake varies with particle-phase behavior, hygroscopic growth factors (HGFs) of nine laboratory-generated, organic and organic–inorganic aerosol systems with physical states ranging from well-mixed liquids to phase-separated particles to viscous liquids or semi-solids were measured with the Differential Aerosol Sizing and Hygroscopicity Spectrometer Probe at RH values ranging from 40 to 90%. Water-uptake measurements were accompanied by HGF and RH-dependent thermodynamic equilibrium calculations using the...

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