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

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Mostrando recursos 1 - 20 de 3,655

1. 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...

2. The Sierra Nevada: Central California's arc - Saleeby, Jason

3. Tectonic significance of serpentinite mobility and ophiolitic melange - Saleeby, Jason B.
Serpentinite is known to be an important constituent of oceanic crust and is particularly abundant along zones of primary structural weakness. Such primary weaknesses occur along fracture zones where large ultramafic massifs are commonly exposed, and along ridge-parallel serpentinite belts that are emplaced near slow-spreading ridges. Tectonic disruption of newly formed crust along transform segments of fracture zones in conjunction with, and followed by, the solid state injection of serpentinitic rocks leads to the development of serpentinite-matrix melange as a primary constituent of oceanic crust. Slumping of rocks along transform axial deep walls and ponding of pelagic and, locally, turbiditic...

4. On the structure of wall turbulence in the thermally neutral atmospheric surface layer - Guala, Michele; LeHew, Jeff; Metzger, Meredith; McKeon, Beverley J.
Recent experimental investigations of the canonical turbulent boundary layer at high Reynolds numbers has provided evidence on the active role of very large-scale structures, extending in the streamwise direction for several boundary layer heights, and modulating near-wall turbulence from the energy containing eddy scales down to the dissipative scales. However, the physical mechanisms governing such interactions are not completely clear yet, and the reason may be related to the fact that the structure of wall turbulence at high Reynolds numbers still deserves further investigation. In this contribution we present recent results on the structural population in wall turbulence. We compare statistical trends obtained in two very...

5. Location of the Termination Shock at Solar Maximum - Stone, E. C.; Cummings, A. C.
During the recent solar maximum, Voyager 1 was beyond 80 AU. Extrapolation of the small gradients of anomalous cosmic rays at solar minimum and the larger gradients at solar maximum indicate that the solar wind termination shock is at ≲ 92 AU at the beginning of 2002.

6. Isotopic abundances in the solar corona as inferred from ACE measurements of solar energetic particles - Leske, R. A.; Mewaldt, R. A.; Cohen, C. M. S.; Christian, E. R.; Cummings, A. C.; Slocum, P. L.; Stone, E. C.; von Rosenvinge, T. T.; Wiedenbeck, M. E.
The isotopic composition of solar energetic particles (SEPs) has been measured using the Solar Isotope Spectrometer on the Advanced Composition Explorer. The measurements include up to 12 isotope abundance ratios for ten elements from C through Ni at energies of tens of MeV/nucleon in 18 large SEP events that have occurred since November 1997. These measurements clearly establish that SEP isotopic composition can vary widely (by factors of >3) from event to event, presumably due to mass fractionation processes during particle acceleration and/or transport. Elemental and isotopic abundance ratios are strongly correlated, suggesting that elemental and isotopic fractionation relative to...

7. Cosmic Ray Source Abundances and the Acceleration of Cosmic Rays - George, J. S.; Wiedenbeck, M. E.; Barghouty, A. F.; Binns, W. R.; Christian, E. R.; Cummings, A. C.; Hink, P. L.; Klarmann, J.; Leske, R. A.; Lijowski, M.; Mewaldt, R. A.; Stone, E. C.; von Rosenvinge, T. T.; Yanasak, N. E.
The galactic cosmic ray elemental source abundances display a fractionation that is possibly based on first ionization potential (FIP) or volatility. A few elements break the general correlation of FIP and volatility and the abundances of these may help to distinguish between models for the origin of the cosmic ray source material. Data from the Cosmic Ray Isotope Spectrometer instrument on NASA’s Advanced Composition Explorer spacecraft were used to derive source abundances for several of these elements (Na, Cu, Zn, Ga, Ge). Three (Na, Cu, Ge) show depletions which could be consistent with a volatility-based source fractionation model.

8. Geology and petrotectonic significance of crystalline rocks of the southernmost Sierra Nevada, California - Sams, David B.; Saleeby, Jason B.
Crystalline rocks of the southernmost Sierra Nevada north of the Garlock fault consist primarily of Early Cretaceous orthogneisses with subordinate paragneiss, and a mid-Cretaceous tonalite batholith complex with coeval gabbroic intrusives. Quartz-rich metasedimentary rocks and marble constitute the main framework into which the plutonic rocks were emplaced. The orthogneisses are predominantly tonalitic in composition with significant layers and domains of granodioritic to granitic, and dioritic to gabbroic gneiss. Field relations, isotopic Rb/Sr, O, and zircon U/Pb data demonstrate assimilation of metasedimentary material into the orthogneisses and magma mixing between mafic, tonalitic, and anatectic granitic magma derived from the metasedimentary material. The orthogneisses yield a family of internally, and externally...

9. Oxygen chemistry in the Venus middle atmosphere - Mills, F. P.; Sundaram, M.; Slanger, T. G.; Allen, M.; Yung, Y. L.
Decades of research have sought to understand the similarities and differences between Venus and Earth. Yet, it is still not clear what chemical processes maintain the long-term stability of Venus' primarily CO_2 atmosphere because, until recently, the observed limit on O_2 was an order of magnitude smaller than predicted by photochemical model calculations. CO_2 dissociates into CO and O after absorbing photons at wavelengths <205 nm. These O atoms should combine to form O_2, and observations of intense airglow, produced as oxygen molecules in the O_2 (a^1 Δ) and O_2 (c^1 Σ) states decay radiatively to the ground state, confirm rapid production of O_2 on both day and...

10. Exoplanet Atmospheres and Photochemistry - Seager, S.; Liang, M.-C.; Parkinson, C. D.; Yung, Y. L.
Over 150 extrasolar planets are known to orbit sun-like stars. A growing number of them (9 to date) are transiting “hot Jupiters” whose physical characteristics can be measured. Atmospheres of two of these planets have already been detected. We summarize the atmosphere detections and useful upper limits, focusing on the MOST albedo upper limit and II exosphere detection for IID 209458b as the most relevant for photochemical models. We describe our photochemical model for hot Jupiters and present a summary explanation of the main results: a low gas-phase abundance of hydrocarbons; an absence of hydrocarbon hazes; and a large reservoir...

11. Observations of ^3He-rich Solar Energetic Particle Events with the Solar Isotope Spectrometer - Cohen, C. M. S.; Mewaldt, R. A.; Leske, R. A.; Cummings, A. C.; Stone, E. C.; Slocum, P. L.; Wiedenbeck, M. E.; Christian, E. R.; von Rosenvinge, T. T.
Using ~4 MeV /nucleon solar energetic particle data from the Solar Isotope Spectrometer (SIS) on the Advanced Composition Explorer (ACE), we identify 60 ^3He-rich time periods longer than 5 hours in length. As many of these time periods do not have "classical" impulsive profiles, we classify each event as one of 4 event types (based on the morphology of the event). The time periods have been associated with solar events listed by the Space Environment Center and energetic electron events observed by the Electron, Proton, and Alpha Monitor (EPAM) on ACE. Only half of the events could be associated with an x-ray...

12. Measurements of the Heavy-Ion Elemental and Isotopic Composition in Large Solar Particle Events from ACE - Leske, R. A.; Mewaldt, R. A.; Cohen, C. M. S.; Cummings, A. C.; Stone, E. C.
Using the Solar Isotope Spectrometer (SIS) on the Advanced Composition Explorer (ACE), we have measured the isotopic composition of as many as eleven elements from He through Ni at energies of tens of MeV /nucleon in eleven solar energetic particle (SEP) events that have occurred since November 1997. We find that isotopic composition varies dramatically from event to event. For example, the ^(22)Ne/^(20)Ne ratio ranges from ~ 0. 7 to > 2 times the solar wind value, being lowest for iron-poor events and highest for iron-rich events. We present the SIS SEP isotope measurements to date and show that the strong...

13. Progress in Tectonic and Petrogenetic Studies in an Exposed Cross-Section of Young (~100 Ma) Continental Crust, Southern Sierra Nevada, California - Saleeby, Jason B.
The southern Sierra Nevada offers an oblique section through young Cordilleran-type batholith generated crust spanning surface (volcanic) to deep (granulitic) levels. Regional mapping and Pb/U zircon geochronology reveal structural continuity through this crustal section for volcanic, plutonic and metamorphic assemblages developed at ~100 Ma, making it one of the youngest sections in the world. Construction of a synthetic cross-section is well-constrained by the oblique section map pattern, abundant age data, and a published crustal structure section that was based on geophysical and lower crustal xenolith data from across the shallow levels of the batholith. The synthetic cross-section depicts the state...

14. Atmospheric Composition, Chemistry, and Clouds - Mills, Franklin P.; Esposito, Larry W.; Yung, Yuk L.
Venus’ atmosphere has a rich chemistry involving interactions among sulfur, chlorine, nitrogen, hydrogen, and oxygen radicals. The chemical regimes in the atmosphere range from ion-neutral reactions in the ionosphere to photochemistry in the middle atmosphere to thermal equilibrium chemistry and surface-atmosphere reactions in the lower atmosphere. This variety makes Venus an important planet to understand within the context of terrestrial-like planets, both in our own solar system and outside it. The primary chemical cycles are believed known but surprisingly few details about these cycles have been fully verified by concurrence among observations, experiments, and modeling. Good models have been developed that account for many properties of the cloud layers,...

15. The Wonder of Life in Its Chemical Aspect - Tirrell, David A.
Hermann Staudinger was deeply interested in both macromolecular chemistry and biology. This chapter reviews briefly the shared origins of studies of natural and synthetic polymers, the subsequent divergence of the two fields, and their more recent convergence, made possible by the development of recombinant DNA methodology. The use of recombinant DNA technology to prepare well-defined macromolecular materials is discussed, along with the use of non-canonical amino acids as probes of protein synthesis in complex cellular systems.

16. Io, its Atmosphere and Optical Emissions - Brown, R. A.; Yung, Y. L.
Io is surrounded by a halo of atoms which radiate in emission lines. This was discovered by groundbased observations in 1973, a year before Pioneer 10 passed through the Jovian system. Earlier optical and radio observers had reported other anomalies associated with Io, and the Pioneer spacecraft discovered an ultraviolet emission cloud around the satellite and a substantial ionosphere. A new field of planetary research is dedicated to integrating these phenomena into a model of Io and of the Jovian environment with which it strongly interacts. Sodium dominates the optical emission cloud around Io. The production rate is very large and...

17. Some Objects Are More Equal Than Others: Measuring and Predicting Importance - Spain, Merrielle; Perona, Pietro
We observe that everyday images contain dozens of objects, and that humans, in describing these images, give different priority to these objects. We argue that a goal of visual recognition is, therefore, not only to detect and classify objects but also to associate with each a level of priority which we call 'importance'. We propose a definition of importance and show how this may be estimated reliably from data harvested from human observers. We conclude by showing that a first-order estimate of importance may be computed from a number of simple image region measurements and does not require access to...

18. Late Cretaceous-Paleocene Extensional Collapse and Disaggregation of the Southernmost Sierra Nevada Batholith - Wood, David J.; Saleeby, Jason
Geobarometric studies have documented that most of the metasedimentary wall rocks and plutons presently exposed in the southernmost Sierra Nevada batholith south of the Lake Isabella area were metamorphosed and emplaced at crustal levels significantly deeper (~15 to 30 km) than the batholithic rocks exposed to the north (depths of ~3 to 15 km). Field and geophysical studies have suggested that much of the southernmost part of the batholith is underlain along low-angle faults by the Rand Schist. The schist is composed mostly of metagraywacke that has been metamorphosed at relatively high pressures and moderate temperatures. NNW-trending compositional, age, and isotopic boundaries in the plutonic rocks of the...

19. A Case for Delamination of the Deep Batholithic Crust beneath the Sierra Nevada, California - Ducea, Mihai; Saleeby, Jason
Surface exposures as well as deep-crustal and upper-mantle xenoliths constrain the composition of the lithospheric column beneath the Sierra Nevada mountain range (California) as it resulted from the generation of the Mesozoic Sierra Nevada batholith (SNB). After the cessation of magmatism at ~80 Ma, the SNB consisted of a ~30 to 35 km thick granitic crust underlain by a batholithic "root," a ~70 km thick sequence of mafic-ultramafic, mainly eclogite-facies cumulate and residues. The deeper root assemblages consist largely of garnet and pyroxenes that precipitated as igneous cumulate phases during the SNB magrnatism. The root assemblages were present beneath the SNB as recently as ~8 to 12...

20. A rift-edge facies of the Late Jurassic Rogue–Chetco arc and Josephine ophiolite, Klamath Mountains, Oregon - Yule, J. Douglas; Saleeby, Jason; Barnes, Calvin G.
The western Jurassic belt of the Klamath Mountains represents one of the Earth's best-preserved exposures of ancient marginal ocean basin lithosphere and chiefly consists of the coeval Rogue–Chetco volcanic-plutonic oceanic arc and Josephine ophiolite. This Late Jurassic ocean basin is hypothesized to have formed in response to rifting that initiated at ca. 165 Ma along the western margin of North America, disrupting a Middle Jurassic arc that had been constructed on older Klamath terranes and forming a marginal ocean basin with an active arc, inter-arc basin, and remnant arc. Previous workers characterized a “rift-edge” facies in the remnant-arc region. This...

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