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Caltech Authors (105,723 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 41,010

1. Rayleigh wave dispersion measurements reveal low-velocity zones beneath the new crust in the Gulf of California - Persaud, Patricia; Di Luccio, Francesca; Clayton, Robert W.
Rayleigh wave tomography provides images of the shallow mantle shear wave velocity structure beneath the Gulf of California. Low-velocity zones (LVZs) are found on axis between 26 and 50 km depth beneath the Guaymas Basin but mostly off axis under the other rift basins, with the largest feature underlying the Ballenas Transform Fault. We interpret the broadly distributed LVZs as regions of partial melting in a solid mantle matrix. The pathway for melt migration and focusing is more complex than an axis-centered source aligned above a deeper region of mantle melt and likely reflects the magmatic evolution of rift segments. We...

2. Obscuration-dependent Evolution of Active Galactic Nuclei - Buchner, Johannes; Georgakakis, Antonis; Nandra, Kirpal; Brightman, Murray; Menzel, Marie-Luise; Liu, Zhu; Hsu, Li-Ting; Salvato, Mara; Rangel, Cyprian; Aird, James; Merloni, Andrea; Ross, Nicholas
We aim to constrain the evolution of active galactic nuclei (AGNs) as a function of obscuration using an X-ray-selected sample of ~2000 AGNs from a multi-tiered survey including the CDFS, AEGIS-XD, COSMOS, and XMM-XXL fields. The spectra of individual X-ray sources are analyzed using a Bayesian methodology with a physically realistic model to infer the posterior distribution of the hydrogen column density and intrinsic X-ray luminosity. We develop a novel non-parametric method that allows us to robustly infer the distribution of the AGN population in X-ray luminosity, redshift, and obscuring column density, relying only on minimal smoothness assumptions. Our analysis...

3. High-J CO Sleds in Nearby Infrared Bright Galaxies Observed By Herschel/PACS - Mashian, N.; Sturm, E.; Sternberg, A.; Janssen, A.; Hailey-Dunsheath, S.; Fischer, J.; Contursi, A.; González-Alfonso, E.; Gracia-Carpio, J.; Poglitsch, A.; Veilleux, S.; Davies, R.; Genzel, R.; Lutz, D.; Tacconi, L.; Verma, A.; Weiss, A.; Polisensky, E.; Nikola, T.
We report the detection of far-infrared (FIR) CO rotational emission from nearby active galactic nuclei (AGNs) and starburst galaxies, as well as several merging systems and Ultra-Luminous Infrared Galaxies (ULIRGs). Using the Herschel Photodetector Array Camera and Spectrometer (PACS), we have detected transitions in the J_(upp) = 14–30 range. The PACS CO data obtained here provide the first reference of well-sampled FIR extragalactic CO spectral line energy distributions (SLEDs) for this range. We find a large range in the overall SLED shape, even among galaxies of similar type, demonstrating the uncertainties in relying solely on high-J CO diagnostics to characterize...

4. Protoplanetary Disk Masses in the Young NGC 2024 Cluster - Mann, Rita K.; Andrews, Sean M.; Eisner, Josh A.; Williams, Jonathan P.; Meyer, Michael R.; Di Francesco, James; Carpenter, John M.; Johnstone, Doug
We present the results from a Submillimeter Array survey of the 887 μm continuum emission from the protoplanetary disks around 95 young stars in the young cluster NGC 2024. Emission was detected from 22 infrared sources, with flux densities from ~5 to 330 mJy; upper limits (at 3σ) for the other 73 sources range from 3 to 24 mJy. For standard assumptions, the corresponding disk masses range from ~0.003 to 0.2 M_☉, with upper limits at 0.002–0.01 M_☉. The NGC 2024 sample has a slightly more populated tail at the high end of its disk mass distribution compared to other...

5. First Space-based Microlens Parallax Measurement of an Isolated Star: Spitzer Observations of OGLE-2014-BLG-0939 - Yee, J. C.; Udalski, A.; Calchi Novati, S.; Gould, A.; Carey, S.; Poleski, R.; Gaudi, B. S.; Pogge, R. W.; Skowron, J.; Kozłowski, S.; Mrόz, P.; Pietrukowicz, P.; Pietrzyński, G.; Szymański, M. K.; Soszyński, I.; Ulaczyk, K.; Wyrzykowski, Ł.
We present the first space-based microlens parallax measurement of an isolated star. From the striking differences in the lightcurve as seen from Earth and from Spitzer (~ 1 AU to the west), we infer a projected velocity v_(hel) ~ 250kms^(-1), which strongly favors a lens in the Galactic Disk with mass M = 0.23 ± 0.07 M_☉ and distance D_L =3.1 ± 0.4 kpc. An ensemble of such measurements drawn from our ongoing program could be used to measure the single-lens mass function including dark objects, and also is necessary for measuring the Galactic distribution of planets since the ensemble...

6. The Effect of Adsorbed Molecule Gas-Phase Deprotonation Enthalpy on Ion Exchange in Sodium Exchanged Zeolites: An In Situ FTIR Investigation - Murphy, Brian; Davis, Mark E.; Xu, Bingjun
Molecular-level understanding of the interactions between reactants and the surface of solid catalysts is of importance to the rational design of catalysts. Here, in situ transmission Fourier transform infrared spectroscopy is employed to investigate the ion exchange between the acidic hydrogen in organic molecules that have been adsorbed from the gas phase and sodium cations in zeolites. Organic compounds with functional groups common among key biomass-derived compounds are used as probe molecules. We demonstrate that ion exchange between acidic hydrogen in organic molecules and the sodium cations in zeolites with the FAU topology produces Brønsted acid sites and the corresponding...

7. On the presence of giant particles downwind of ships in the marine boundary layer - Sorooshian, Armin; Prabhakar, Gouri; Jonsson, Haflidi; Woods, Roy K.; Flagan, Richard C.; Seinfeld, John H.
This study examines large oceangoing ships as a source of giant cloud condensation nuclei (D_p > 2 µm) due to wake and stack emissions off the California coast. Observed particle number concentrations behind 10 ships exceeded those in “control” areas, exhibiting number concentration enhancement ratios (ERs) for minimum threshold diameters of ~2, ~10, and ~20 µm as high as 2.7, 5.5, and 7.5, respectively. ER decreases with increasing downwind distance and altitude. ER becomes better correlated with ship size variables (gross tonnage, length, and beam) as the minimum size threshold increases from 2 to 20 µm, whereas ship speed has a less distinct relationship with...

8. Measurement of the production cross section ratio σ(_(χb2)(1P))/σ(χ_(b1)(1P)) in pp collisions at √s = 8 TeV - Khachatryan, V.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Di Marco, E.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Rogan, C.; Spiropulu, M.; Timciuc, V.; Wilkinson, R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
A measurement of the production cross section ratio σ(χ_(b2)(1P))/σ(χ_(b1)(1P)) is presented. The χ_(b1)(1P) and χ_(b2)(1P) bottomonium states, promptly produced in pp collisions at √s=8 TeV, are detected by the CMS experiment at the CERN LHC through their radiative decays χb_(1,2)(1P)→ϒ(1S)+γ. The emitted photons are measured through their conversion to e^+e^− pairs, whose reconstruction allows the two states to be resolved. The ϒ(1S) is measured through its decay to two muons. An event sample corresponding to an integrated luminosity of 20.7 fb^(−1) is used to measure the cross section ratio in a phase-space region defined by the photon pseudorapidity, |η^γ|<1.0; the...

9. Vernon B. Mountcastle (1918–2015) - Andersen, Richard A.
Vernon Mountcastle, born in 1918 in Shelbyville, Kentucky, was one of the giants of modern systems neuroscience who will be remembered for his ground-breaking research centered on the topics of perception and cognition. His impact on the field of neuroscience has been profound, not only for the discoveries he has made but also for the key role he has played in the founding, promoting, and nurturing of the field through training and service. He has been referred to by some as the father of neuroscience, and long-time Hopkins professor Sol Snyder credits him with producing “the first functional map of...

10. Ridge subduction sparked reorganization of the Pacific plate-mantle system 60-50 million years ago - Seton, Maria; Flament, Nicolas; Whittaker, Joanne; Müller, R. Dietmar; Gurnis, Michael; Bower, Dan J.
A reorganization centered on the Pacific plate occurred ~53–47 million years ago. A “top-down” plate tectonic mechanism, complete subduction of the Izanagi plate, as opposed to a “bottom-up” mantle flow mechanism, has been proposed as the main driver. Verification based on marine geophysical observations is impossible as most ocean crust recording this event has been subducted. Using a forward modeling approach, which assimilates surface plate velocities and shallow thermal structure of slabs into mantle flow models, we show that complete Izanagi plate subduction and margin-wide slab detachment induced a major change in sub-Pacific mantle flow, from dominantly southward before 60 Ma to...

11. On the variability in fracture toughness of ‘ductile’ bulk metallic glasses - Narayan, R. L.; Tandaiya, Parag; Garrett, G. R.; Demetriou, M. D.; Ramamurty, U.
The mode I fracture toughness, K_(Ic), of ductile bulk metallic glasses (BMGs) exhibits a high degree of specimen-to-specimen variability. By conducting fracture experiments in modes I and II, we demonstrate that the observed high variability in mode I, vis-à-vis mode II, is a result of highly variable propensity for the conversion of shear bands into cracks in mode I whereas in mode II, crack growth direction is fixed. Thus, the measured variability in K_(Ic) is intrinsic to the nature of BMGs.

12. Idiosyncratic Brain Activation Patterns Are Associated with Poor Social Comprehension in Autism - Byrge, Lisa; Dubois, Julien; Tyszka, J. Michael; Adolphs, Ralph; Kennedy, Daniel P.
Autism spectrum disorder (ASD) features profound social deficits but neuroimaging studies have failed to find any consistent neural signature. Here we connect these two facts by showing that idiosyncratic patterns of brain activation are associated with social comprehension deficits. Human participants with ASD (N = 17) and controls (N = 20) freely watched a television situation comedy (sitcom) depicting seminaturalistic social interactions (“The Office”, NBC Universal) in the scanner. Intersubject correlations in the pattern of evoked brain activation were reduced in the ASD group—but this effect was driven entirely by five ASD subjects whose idiosyncratic responses were also internally unreliable....

13. Interrogation of the Megathrust Zone in the Tohoku-Oki Seismic Region by Waveform Complexity: Intraslab Earthquake Rupture and Reactivation of Subducted Normal Faults - Lui, Semechah K. Y.; Helmberger, Don; Wei, Shengji; Huang, Yihe; Graves, Robert W.
Results from the 2011 Mw 9.1 Tohoku-Oki megathrust earthquake display a complex rupture pattern, with most of the high-frequency energy radiated from the downdip edge of the seismogenic zone and very little from the large shallow rupture. Current seismic results of smaller earthquakes in this region are confusing due to disagreements among event catalogs on both the event locations (>30 km horizontally) and mechanisms. Here we present an in-depth study of a series of intraslab earthquakes that occurred in a localized region near the downdip edge of the main shock. We explore the validity of 1D velocity model and refine...

14. Upper tropospheric ozone production from lightning NO_x-impacted convection: Smoke ingestion case study from the DC3 campaign - Apel, E. C.; Wennberg, P. O.; Crounse, J. D.
As part of the Deep Convective Cloud and Chemistry (DC3) experiment, the National Science Foundation/National Center for Atmospheric Research (NCAR) Gulfstream-V (GV) and NASA DC-8 research aircraft probed the chemical composition of the inflow and outflow of two convective storms (north storm, NS, south storm, SS) originating in the Colorado region on 22 June 2012, a time when the High Park wildfire was active in the area. A wide range of trace species were measured on board both aircraft including biomass burning (BB) tracers hydrogen cyanide (HCN) and acetonitrile (ACN). Acrolein, a much shorter lived tracer for BB, was also...

15. Mars Reconnaissance Orbiter and Opportunity observations of the Burns formation: Crater hopping at Meridiani Planum - Arvidson, R. E.; Bell, J. F., III; Catalano, J. G.; Clark, B. C.; Fox, V. K.; Gellert, R.; Grotzinger, J. P.; Guinness, E. A.; Herkenhoff, K. E.; Knoll, A. H.; Lapotre, M. G. A.; McLennan, S. M.; Ming, D. W.; Morris, R. V.; Murchie, S. L.; Powell, K. E.; Smith, M. D.; Squyres, S. W.; Wolff, M. J.; Wray, J. J.
Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral (1.0–2.65 µm) along-track oversampled observations covering Victoria, Santa Maria, Endeavour, and Ada craters were processed to 6 m/pixel and used in combination with Opportunity observations to detect and map hydrated Mg and Ca sulfate minerals in the Burns formation. The strongest spectral absorption features were found to be associated with outcrops that are relatively young and fresh (Ada) or preferentially scoured of dust, soil, and coatings by prevailing winds. At Victoria and Santa Maria, the scoured areas are on the southeastern rims and walls, opposite to the sides where wind-blown sands extend out of the...

16. On the rate of convergence for critical crossing probabilities - Binder, I.; Chayes, L.; Lei, H. K.
For the site percolation model on the triangular lattice and certain generalizations for which Cardy’s Formula has been established we acquire a power law estimate for the rate of convergence of the crossing probabilities to Cardy’s Formula.

17. Search for stealth supersymmetry in events with jets, either photons or leptons, and low missing transverse momentum in pp collisions at 8 TeV - Khachatryan, V.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Pierini, M.; Spiropulu, M.; Vlimant, J. R.; Wilkinson, R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
The results of a search for new physics in final states with jets, either photons or leptons, and low missing transverse momentum are reported. The study is based on a sample of proton–proton collisions collected at a center-of-mass energy √s=8 TeV with the CMS detector in 2012. The integrated luminosity of the sample is 19.7 fb^(−1). Many models of new physics predict the production of events with jets, electroweak gauge bosons, and little or no missing transverse momentum. Examples include stealth models of supersymmetry (SUSY), which predict a hidden sector at the electroweak energy scale in which SUSY is approximately...

18. Avoiding Progenitor Bias: The Structural and Mass Evolution of Brightest Group and Cluster Galaxies in Hierarchical Models since z≾1 - Shankar, Francesco; Buchan, Stewart; Rettura, Alessandro; Bouillot, Vincent R.; Moreno, Jorge; Licitra, Rossella; Bernardi, Mariangela; Huertas-Company, Marc; Mei, Simona; Ascaso, Begoña; Sheth, Ravi; Delaye, Lauriane; Raichoor, Anand
The mass and structural evolution of massive galaxies is one of the hottest topics in galaxy formation. This is because it may reveal invaluable insights into the still debated evolutionary processes governing the growth and assembly of spheroids. However, direct comparison between models and observations is usually prevented by the so-called progenitor bias, i.e., new galaxies entering the observational selection at later epochs, thus eluding a precise study of how pre-existing galaxies actually evolve in size. To limit this effect, we here gather data on high-redshift brightest group and cluster galaxies, evolve their (mean) host halo masses down to z...

19. Evolution of vertebrates as viewed from the crest - Green, Stephen A.; Simões-Costa, Marcos; Bronner, Marianne E.
The origin of vertebrates was accompanied by the advent of a novel cell type: the neural crest. Emerging from the central nervous system, these cells migrate to diverse locations and differentiate into numerous derivatives. By coupling morphological and gene regulatory information from vertebrates and other chordates, we describe how addition of the neural-crest-specification program may have enabled cells at the neural plate border to acquire multipotency and migratory ability. Analysis of the topology of the neural crest gene regulatory network can serve as a useful template for understanding vertebrate evolution, including elaboration of neural crest derivatives.

20. Long-term atomistic simulation of hydrogen diffusion in metals - Wang, K. G.; Ortiz, M.; Ariza, M. P.
Whereas great strides have been taken towards the characterization of metal-based nanomaterials for high-speed, high capacity, reversible hydrogen storage applications, most mesoscopic approaches to date have relied on molecular dynamics (MD) as their chief representational and computational paradigm. However, the absorption and desorption of hydrogen in nanomaterials is characterized by an atomic, deformation-diffusion coupled process with a time scale of the order of seconds to hours–far beyond the characteristic time windows of MD-based simulations. In this work, we present an application of a novel deformation-diffusion coupled computational framework, which allows the long-term simulation of such slow processes and at the...

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