Recursos de colección

Caltech Authors (127.665 recursos)

Repository of works by Caltech published authors.

Type = Article

Mostrando recursos 1 - 20 de 48.665

  1. Reprogramming of avian neural crest axial identity and cell fate

    Simões-Costa, Marcos; Bronner, Marianne E.
    Neural crest populations along the embryonic body axis of vertebrates differ in developmental potential and fate, so that only the cranial neural crest can contribute to the craniofacial skeleton in vivo. We explored the regulatory program that imbues the cranial crest with its specialized features. Using axial-level specific enhancers to isolate and perform genome-wide profiling of the cranial versus trunk neural crest in chick embryos, we identified and characterized regulatory relationships between a set of cranial-specific transcription factors. Introducing components of this circuit into neural crest cells of the trunk alters their identity and endows these cells with the ability...

  2. Biomimetic Accommodating Intraocular Lens Using a Valved Deformable Liquid Balloon

    DeBoer, Charles M. T.; Lee, Jonathan K.; Wheelan, Brooks P.; Cable, Craig; Shi, Wendian; Tai, Yu-Chong; Humayun, Mark S.
    Objective: Presbyopia is a common age-related condition that prevents people from focusing on near objects. The etiology of presbyopia continues to be debated, but the end effect of all postulated mechanisms is the lack of deformation of the human lens. Using our understanding of the biomechanical properties of the natural human lens, we created a unique accommodating intraocular lens. Although this lens can be used for lenticular disease such as myopia and hyperoperopia, this study addresses the needs of cataract patients with presbyopia. Methods: The lens was implanted into presbyopic human cadaver eyes. Focal length of the lens was measured...

  3. Resolving Fine-Scale Heterogeneity of Co-seismic Slip and the Relation to Fault Structure

    Milliner, C. W. D.; Sammis, C.; Allam, A. A.; Dolan, J. F.; Hollingsworth, J.; Leprince, S.; Ayoub, F.
    Fault slip distributions provide important insight into the earthquake process. We analyze high-resolution along-strike co-seismic slip profiles of the 1992 M_w = 7.3 Landers and 1999 M_w = 7.1 Hector Mine earthquakes, finding a spatial correlation between fluctuations of the slip distribution and geometrical fault structure. Using a spectral analysis, we demonstrate that the observed variation of co-seismic slip is neither random nor artificial, but self-affine fractal and rougher for Landers. We show that the wavelength and amplitude of slip variability correlates to the spatial distribution of fault geometrical complexity, explaining why Hector Mine has a smoother slip distribution as it occurred on a...

  4. Understanding thermoelectric properties from high-throughput calculations: trends, insights, and comparisons with experiment

    Chen, Wei; Pöhls, Jan-Hendrik; Hautier, Geoffroy; Broberg, Danny; Bajaj, Saurabh; Aydemir, Umut; Gibbs, Zachary M.; Zhu, Hong; Asta, Mark; Snyder, G. Jeffrey; Meredig, Bryce; White, Mary Anne; Persson, Kristin; Jain, Anubhav
    We present an overview and preliminary analysis of computed thermoelectric properties for more than 48 000 inorganic compounds from the Materials Project (MP). We compare our calculations with available experimental data to evaluate the accuracy of different approximations in predicting thermoelectric properties. We observe fair agreement between experiment and computation for the maximum Seebeck coefficient determined with MP band structures and the BoltzTraP code under a constant relaxation time approximation (R^2 = 0.79). We additionally find that scissoring the band gap to the experimental value improves the agreement. We find that power factors calculated with a constant and universal relaxation...

  5. Probing Molecular Shape. 1. Conformational Studies of 5-Hydroxyhexahydropyrimidine and Related Compounds

    Locke, Julie M.; Crumbie, Robyn L.; Griffith, Renate; Bailey, Trevor D.; Boyd, Susan; Roberts, John D.
    Understanding the factors that determine molecular shape enables scientists to begin to understand and tailor molecular properties and reactivity. Many biomolecules and bioactive compounds contain aliphatic heterocyclic rings whose conformations play a major role in their biological activity. The interplay of a number of factors, both steric and electronic, is examined for 5-hydroxyhexahydropyrimidine (1) and related compounds with use of spectroscopy and molecular modeling.

  6. Organic nitrate chemistry and its implications for nitrogen budgets in an isoprene- and monoterpene-rich atmosphere: constraints from aircraft (SEAC^4RS) and ground-based (SOAS) observations in the Southeast US

    Fisher, Jenny A.; Wennberg, Paul O.; Crounse, John D.; Teng, Alex P.; Nguyen, Tran B.; St. Clair, Jason M.
    Formation of organic nitrates (RONO_2) during oxidation of biogenic volatile organic compounds (BVOCs: isoprene, monoterpenes) is a significant loss pathway for atmospheric nitrogen oxide radicals (NO_x), but the chemistry of RONO_2 formation and degradation remains uncertain. Here we implement a new BVOC oxidation mechanism (including updated isoprene chemistry, new monoterpene chemistry, and particle uptake of RONO_2) in the GEOS-Chem global chemical transport model with  ∼  25  ×  25 km^2 resolution over North America. We evaluate the model using aircraft (SEAC^4RS) and ground-based (SOAS) observations of NO_x, BVOCs, and RONO_2 from the Southeast US in summer 2013. The updated simulation successfully reproduces the concentrations of...

  7. Imaging spectroscopy of geological samples and outcrops: Novel insights from microns to meters

    Greenberger, Rebecca N.; Mustard, John F.; Ehlmann, Bethany L.; Blaney, Diana L.; Cloutis, Edward A.; Wilson, Janette H.; Green, Robert O.; Fraeman, Abigail A.
    Imaging spectroscopy is a powerful, non-destructive mineralogic tool that provides insights into a variety of geological processes. This remote measurement technique has been used for decades from orbital or aerial platforms to characterize surface compositions of Earth and other solar system bodies. These instruments have now been miniaturized for use in the laboratory and field, thereby enabling petrologic analyses of samples and outcrops. Here, we review the technique and present four examples showing the exciting science potential and new insights into geological processes.

  8. Spitzer Microlensing Program as a Probe for Globular Cluster Planets. Analysis of OGLE-2015-BLG-0448

    Poleski, Radosław; Novati, Sebastiano Calchi; Beichman, C.
    The microlensing event OGLE-2015-BLG-0448 was observed by Spitzer and lay within the tidal radius of the globular cluster NGC 6558. The event had moderate magnification and was intensively observed, hence it had the potential to probe the distribution of planets in globular clusters. We measure the proper motion of NGC 6558 µ_(cl)(N,E)=(+0.36 ± 0.10,+1.42 ± 0.10, + yr^(-1)) as well as the source and show that the lens is not a cluster member. Even though this particular event does not probe the distribution of planets in globular clusters, other potential cluster lens events can be verified using our methodology. Additionally,...

  9. Photo-reverberation Mapping of a Protoplanetary Accretion Disk around a T Tauri Star

    Meng, Huan Y. A.; Plavchan, Peter; Rieke, George H.; Cody, Ann Marie; Güth, Tina; Stauffer, John; Covey, Kevin; Carey, Sean; Ciardi, David; Duran-Rojas, Maria C.; Gutermuth, Robert A.; Morales-Calderón, María; Rebull, Luisa M.; Watson, Alan M.
    Theoretical models and spectroscopic observations of newborn stars suggest that protoplantary disks have an inner "wall" at a distance set by the disk interaction with the star. Around T Tauri stars, the size of this disk hole is expected to be on a 0.1 au scale that is unresolved by current adaptive optics imaging, though some model-dependent constraints have been obtained by near-infrared interferometry. Here we report the first measurement of the inner disk wall around a solar-mass young stellar object, YLW 16B in the ρ Ophiuchi star-forming region, by detecting the light-travel time of the variable radiation from the...

  10. The Collapse of the Wien Tail in the Coldest Brown Dwarf? Hubble Space Telescope Near-Infrared Photometry of WISE J085510.83-071442.5

    Schneider, Adam C.; Cushing, Michael C.; Kirkpatrick, J. Davy; Gelino, Christopher R.
    We present Hubble Space Telescope (HST) near-infrared photometry of the coldest known brown dwarf, WISE J085510.83−071442.5 (WISE 0855−0714). WISE 0855−0714 was observed with the Wide Field Camera 3 (WFC3) on board HST using the F105W, F125W, and F160W filters, which approximate the Y, J, and H near-infrared bands. WISE 0855−0714 is undetected at F105W with a corresponding 2σ magnitude limit of ~26.9. We marginally detect WISE 0855−0714 in the F125W images (S/N ~ 4), with a measured magnitude of 26.41 ± 0.27, more than a magnitude fainter than the J-band magnitude reported by Faherty et al. WISE J0855−0714 is clearly...

  11. Planetary Candidates Observed by Kepler. VII. The First Fully Uniform Catalog Based on the Entire 48-month Data Set (Q1–Q17 DR24)

    Coughlin, Jeffrey L.; Akeson, Rachel; Christiansen, Jessie L.; Ramirez, Solange
    We present the seventh Kepler planet candidate (PC) catalog, which is the first catalog to be based on the entire, uniformly processed 48-month Kepler data set. This is the first fully automated catalog, employing robotic vetting procedures to uniformly evaluate every periodic signal detected by the Q1–Q17 Data Release 24 (DR24) Kepler pipeline. While we prioritize uniform vetting over the absolute correctness of individual objects, we find that our robotic vetting is overall comparable to, and in most cases superior to, the human vetting procedures employed by past catalogs. This catalog is the first to utilize artificial transit injection to...

  12. The Herschel Orion Protostar Survey: Spectral Energy Distributions and Fits Using a Grid of Protostellar Models

    Furlan, E.; Fischer, W. J.; Ali, B.; Stutz, A. M.; Stanke, T.; Tobin, J. J.; Megeath, S. T.; Osorio, M.; Hartmann, L.; Calvet, N.; Poteet, C. A.; Booker, J.; Manoj, P.; Watson, D. M.; Allen, L.
    We present key results from the Herschel Orion Protostar Survey: spectral energy distributions (SEDs) and model fits of 330 young stellar objects, predominantly protostars, in the Orion molecular clouds. This is the largest sample of protostars studied in a single, nearby star formation complex. With near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and submillimeter photometry from APEX, our SEDs cover 1.2–870 μm and sample the peak of the protostellar envelope emission at ~100 μm. Using mid-IR spectral indices and bolometric temperatures, we classify our sample into 92 Class 0 protostars, 125 Class I protostars, 102...

  13. A Coherent Study of Emission Lines from Broadband Photometry: Specific Star Formation Rates and [O III]/Hβ Ratio at 3 < z < 6

    Faisst, A. L.; Capak, P.; Hsieh, B. C.; Laigle, C.; Salvato, M.; Tasca, L.; Cassata, P.; Davidzon, I.; Ilbert, O.; Le Fèvre, O.; Masters, D.; McCracken, H. J.; Steinhardt, C.; Silverman, J. D.; de Barros, S.; Hasinger, G.; Scoville, N. Z.
    We measure the Hα and [O III] emission line properties as well as specific star formation rates (sSFRs) of spectroscopically confirmed 3 < z < 6 galaxies in COSMOS from their observed colors versus redshift evolution. Our model describes consistently the ensemble of galaxies including intrinsic properties (age, metallicity, star formation history), dust attenuation, and optical emission lines. We forward-model the measured Hα equivalent widths (EW) to obtain the sSFR out to z ~ 6 without stellar mass fitting. We find a strongly increasing rest-frame Hα EW that is flattening off above z ~ 2.5 with average EWs of 300–600...

  14. Two Stars Two Ways: Confirming a Microlensing Binary Lens Solution with a Spectroscopic Measurement of the Orbit

    Yee, Jennifer C.; Johnson, John Asher; Skowron, Jan; Gould, Andrew; Pineda, J. Sebastian; Eastman, Jason; Vanderburg, Andrew; Howard, Andrew
    Light curves of microlensing events involving stellar binaries and planetary systems can provide information about the orbital elements of the system due to orbital modulations of the caustic structure. Accurately measuring the orbit in either the stellar or planetary case requires detailed modeling of subtle deviations in the light curve. At the same time, the natural, Cartesian parameterization of a microlensing binary is partially degenerate with the microlens parallax. Hence, it is desirable to perform independent tests of the predictions of microlens orbit models using radial velocity (RV) time series of the lens binary system. To this end, we present...

  15. Hα Imaging of Nearby Seyfert Host Galaxies

    Theios, Rachel L.; Malkan, Matthew A.; Ross, Nathaniel R.
    We used narrowband (Δλ = 70 Å) interference filters with the CCD imaging camera on the Nickel 1.0 m telescope at Lick Observatory to observe 31 nearby (z < 0.03) Seyfert galaxies in the 12 μm active galaxy sample. We obtained pure emission-line images of each galaxy, which reach down to a flux limit of 7.3 × 10^(−15) erg cm^(−2) s^(−1) arcsec^(−2), and corrected these images for [N ii] emission and extinction. We separated the Hα emission line of the "nucleus" (central 100–1000 pc) from that of the host galaxy. The extended Hα emission is expected to be powered by...

  16. ISM excitation and metallicity of star-forming galaxies at z ~ 3.3 from near-IR spectroscopy

    Onodera, M.; Carollo, C. M.; Lilly, S.; Renzini, A.; Arimoto, N.; Capak, P.; Daddi, E.; Scoville, N.; Tacchella, S.; Tatehora, S.; Zamorani, G.
    We study the relationship between stellar mass, star formation rate (SFR), ionization state, and gas-phase metallicity for a sample of 41 normal star-forming galaxies at 3 ≾ z ≾ 3.7. The gas-phase oxygen abundance, ionization parameter, and electron density of ionized gas are derived from rest-frame optical strong emission lines measured on near-infrared spectra obtained with Keck/Multi-Object Spectrograph for Infra-Red Exploration. We remove the effect of these strong emission lines in the broadband fluxes to compute stellar masses via spectral energy distribution fitting, while the SFR is derived from the dust-corrected ultraviolet luminosity. The ionization parameter is weakly correlated with...

  17. A Scalable Turbulent Mixing Aerosol Reactor for Oxide-Coated Silicon Nanoparticles

    Holunga, Dean M.; Flagan, Richard C.; Atwater, Harry A.
    A new, turbulent flow aerosol reactor is described that enables synthesis of uniformly sized aerosol nanoparticles during a residence time of a few milliseconds. The short residence time allows processing of high number concentration aerosols, in excess of 10^9 cm^(-3), to be processed with minimal coagulation, leading to an aerosol throughput approaching 10^(11) particles cm^(-3) s^(-1). Turbulent mixing speeds thermal and chemical transport beyond diffusional limits inherent in laminar flow reactors, providing the thermal energy to drive chemical reactions, coalescence, densification, and crystallization of particles. With enhanced transport, residence time in the reactor can be reduced, thus limiting coagulate particle...

  18. Rest-UV Absorption Lines as Metallicity Estimator: the Metal Content of Star-Forming Galaxies at z ~ 5

    Faisst, A. L.; Capak, P. L.; Davidzon, I.; Salvato, M.; Laigle, C.; Ilbert, O.; Onodera, M.; Hasinger, G.; Kakazu, Y.; Masters, D.; McCracken, H. J.; Mobasher, B.; Sanders, D.; Silverman, J. D.; Yan, L.; Scoville, N. Z.
    We measure a relation between the depth of four prominent rest-UV absorption complexes and metallicity for local galaxies and verify it up to z ~ 3. We then apply this relation to a sample of 224 galaxies at 3.5 < z < 6.0 ( 〈z〉 = 4.8) in the Cosmic Evolution Survey (COSMOS), for which unique UV spectra from the Deep Imaging Multi-object Spectrograph (DEIMOS) and accurate stellar masses from the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) are available. The average galaxy population at z ~ 5 and log(M/M_☉) > 9 is characterized by 0.3–0.4 dex (in units of...

  19. Major disruption of D″ beneath Alaska

    Sun, Daoyuan; Helmberger, Don; Miller, Meghan S.; Jackson, Jennifer M.
    D″ represents one of the most dramatic thermal and compositional layers within our planet. In particular, global tomographic models display relatively fast patches at the base of the mantle along the circum-Pacific which are generally attributed to slab debris. Such distinct patches interact with the bridgmanite (Br) to post-bridgmanite (PBr) phase boundary to generate particularly strong heterogeneity at their edges. Most seismic observations for the D″ come from the lower mantle S wave triplication (Scd). Here we exploit the USArray waveform data to examine one of these sharp transitions in structure beneath Alaska. From west to east beneath Alaska, we...

  20. CLASH: Joint Analysis of Strong-Lensing, Weak-Lensing Shear and Magnification Data for 20 Galaxy Clusters

    Umetsu, Keiichi; Zitrin, Adi; Gruen, Daniel; Merten, Julian; Donahue, Megan; Postman, Marc
    We present a comprehensive analysis of strong-lensing, weak-lensing shear and magnification data for a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 ≾ z ≾ 0.69 selected from Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis combines constraints from 16-band Hubble Space Telescope observations and wide-field multi-color imaging taken primarily with Suprime-Cam on the Subaru Telescope, spanning a wide range of cluster radii (10"–16'). We reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all of the clusters. We find the...

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.