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rss_1.0 Recursos de colección

Caltech Authors (82.845 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 3.332

1. Pliocene volcanogenic sedimentation along an accommodation zone in northeastern Baja California: The Puertecitos Formation - Martín-Barajas, Arturo; Tellez-Duarte, Miguel; Stock, Joann M.
Accommodation zones on rift systems produce distinctive sedimentary facies and facies architecture. The Puertecitos volcanic province in the northern Gulf Extensional Province comprises an accommodation zone and records marine sedimentation and explosive volcanism during upper Miocene and early Pliocene time. The volcano-sedimentary sequence consists of two ·westward-thinning, wedge-shaped transgressive-regressive marine sequences, each less than 100 m thick, separated by one large pyroclastic flow unit. Northward the lower member is separated from the upper member by an angular unconformity and/or an interval of subaerial erosion. To the southeast, the volcanic units dominate the stratigraphic sections, whereas northward the two marine sequences dominate and contain the distal volcaniclastic facies. We propose the...

2. Pacific North America plate tectonics of the Neogene southwestern United States: An update - Atwater, Tanya; Stock, Joann
We use updated rotations within the Pacific-Antarctica-Africa-North America plate circuit to calculate Pacific-North America plate reconstructions for times since chron 13 (33 Ma). The direction of motion of the Pacific plate relative to stable North America was fairly steady between chrons 13 and 4, and then changed and moved in a more northerly direction from chron 4 to the present (8 Ma to the present). No Pliocene changes in Pacific-North America plate motion are resolvable in these data, suggesting that Pliocene changes in deformation style along the boundary were not driven by changes in plate motion. However, the chron 4 change in Pacific-North America plate motion appears...

3. Voyager Investigation of the Saturnian System - Stone, E. C.
A brief review of the objectives and capabilities of the Voyager mission at Saturn is provided. In addition to a description of the eleven Voyager investigations and the Saturn encounter geometry, the scientific capabilities are discussed in the areas of atmospheric, satellite, magnetospheric, and ring studies.

4. Radial Development of a Solar Cosmic Ray Event Between 0.4 and 1 AU on March 3, 1975 as Observed from HELIOS 1 and IMP-7 - Wibberenz, G.; Kunow, H.; Green, G.; Müller-Mellin, R.; Witte, M.; Hempe, H.; Mewaldt, R. A.; Stone, E. C.; Vogt, R. E.; Reinhard, R.
A micro event was observed by cosmic ray particle experiments on board of Helios 1 and IMP on March 3, 1975. At the time of the event Helios 1 was at a radial distance of 0.4 AU from the sun. The IMP space craft near earth was connected via interplanetary magnetic fieldline with a solar region about 7° west of Helios. The roots of both fieldlines were well within the fast propagation region of two active centers which were capable to accelerate solar particles. This relative position of the two space craft allows to separate solar injection and interplanetary propagation...

5. Remote Monitoring of Shifting Sands and Vegetation Cover in Arid Regions - Ray, Terrill W.; Murray, Bruce C.
A significant factor in the degradation of arid and semi-arid lands is the removal of sand and soil through wind action. Mobilized sand can destroy downwind vegetation through sand blasting and burial. Since vegetation cover is an important factor in determining the erodibility of an area, there is a potential positive feedback that can lead ultimately to the mobilization of larger areas of sand. Mobilized areas of sand in irrigated arid regions can be detected in the visible and near-infrared because of increased albedo and the decreased plant cover, in the thermal infrared due to emissivity differences between the very...

6. Simultaneous Observations of Cosmic Ray Particles in a Corotating Interplanetary Structure at Different Solar Distances between 0.3 and 1 AU from HELIOS 1 and 2 and IMP 7 and 8 - Kunow, H.; Wibberenz, G.; Green, G.; Müller-Mellin, R.; Witte, M.; Hempe, H.
From December 1975 to June 1976 we observed an evolving recurrent proton enhancement with IMP 7/8 and Helios 1/2 at different distances from the sun. The corotating character is established over 4 solar rotations. Due to the unique constellation in March 1976 simultaneous measurements were possible which allowed a study of the radial development undisturbed by temporal effects. The intensity variation of the ~4 - 13 MeV protons between 0.43 and 1 AU revealed a sudden increase to a large positive gradient (+329 %/AU) in the leading edge of the event. This value is consistent with a major source outside 1 AU. We suggest an interplanetary acceleration which becomes sufficiently effective...

7. Early Rift Sedimentation and Structure along the NE Margin of Baja California - Stock, Joann M.; Martín-Barajas, Arturo; Tellez-Duarte, Miguel
This field trip will examine deposits and structures in four basins of NE Baja California which formed during Neogene rifting in the Gulf of California Extensional Province (Fig. 1). Our objective is to provide an overview of depositional environments and facies, and tectonic controls on the basin evolution, as a guide to interpreting early rift basins elsewhere around the Gulf of California as well as at other incipient oceanic rifts. The basins we will visit range in age from middle Miocene (the continental deposits of the Santa Rosa basin) to late Miocene (upper part of the Santa Rosa basin, and the San Felipe marine sequence) to Pliocene (San Felipe marine sequence, Puertecitos Formation,...

8. The Elemental Composition of 4-30 MeV/nuc Cosmic Ray Nuclei with 1 ≤ Z ≤ 8 - Mewaldt, R. A.; Stone, E. C.; Vidor, S. B.; Vogt, R. E.
Recent observations of low energy cosmic rays have shown enhanced fluxes of nitrogen and oxygen relative to other elements in the ~8-30 MeV/nuc energy interval. We have extended the measurements of lithium through oxygen down to ~ 4 MeV/nuc with the Caltech Electron/Isotope Spectrometers on IMP-7 and -8 during solar quiet periods from October 1972 to September 1974. We find no evidence for significant enhancements of Li, Be, B. or C, which are found to have energy spectra consistent with those expected from the adiabatic deceleration of higher energy galactic cosmic rays. The He, N, and O fluxes are greatly enhanced when compared to the other elements, with relative abundances of...

9. Implications of Time Variations for the Origin of Low Energy Cosmic Ray Nitrogen and Oxygen Nuclei - Mewaldt, R. A.; Stone, E. C.; Vogt, R. E.
We report observations of time variations in the quiet time intensity of 5-27 MeV/nuc nitrogen and oxygen and 13-25 MeV/nuc helium nuclei, obtained with the Caltech Electron/Isotope Spectrometers on IMP 7 and 8. We find no significant correlation of the O variations with variations in the low intensity fluxes of 1-2 MeV solar protons. However, we do find the O intensity to be well correlated with the modulation of galactic cosmic rays as measured by neutron monitors. When compared with the neutron monitor, the factor of ~ 3 change in the 0 intensity during 1972 through 1974 is consistent with the factor of ~ 30 increase observed since 1969. These...

10. Observations of Hydrogen and Helium Isotopes in Solar Cosmic Rays - Hurford, G. J.; Stone, E. C.; Vogt, R. E.
Hydrogen and helium isotopes in solar cosmic rays between 1.2 and 15.0 MeV/nuc have been observed with the Ca1tech Electron/Isotope Spectrometer on IMP-7. During 1973 three "^3He rich events", containing more ^3He than ^2H or ^3H, were observed on 14 February, 29 June, and 5 September. The latter event was particularly interesting in that (^3He/^4He) ~ 6 and (^3He/^1H) ~ 1. Excluding these three events, flare-averaged ratios for ^2H/^1H and ^3H/^1H have been obtained for energies below 8.6 MeV/nuc. When compared with the ratios at higher energies, the observed energy dependence is consistent with the thin target model of Ramaty and Kozlovsky with a relativistic pathlength of ~ 1 g/cm^2....

11. Isotopic Composition of the Anomalous Low Energy Cosmic Ray Nitrogen and Oxygen - Mewaldt, R. A.; Stone, E. C.; Vidor, S. B.; Vogt, R. E.
The isotopic composition of the enhanced fluxes of cosmic ray nitrogen and oxygen observed below 30 MeV/nuc is of interest, whether the nuclei are a sample from some nearby galactic source region that is underabundant in carbon, or a sample of the neutral interstellar medium. Enhanced fluxes in the 6 to 12 MeV/nuc energy interval were measured over a two year period with the Caltech Electron/Isotope Spectrometer on IMP-7. The observed low-energy nitrogen and oxygen nuclei are predominantly N-14 and O-16, with upper limits (84% confidence level) of N-15/N below 0.26, O-17/0 below 0.13, and O-18/0 below 0.12 for other...

12. The Isotopic Composition of Hydrogen and Helium in Low Energy Cosmic Rays - Mewaldt, R. A.; Stone, E. C.; Vogt, R. E.
The Caltech Electron/Isotope Spectrometer on IMP-7 has been used to identify the isotopes ^2H and ^3He in low energy cosmic rays during solar quiet periods from October 1972 to October 1974. These observations cover the energy intervals 5 - 29 MeV/nuc for ^2H and 7 - 50 MeV/nuc for ^3He. The energy spectra of ^1H, ^2H and ^3He all fall rapidly with decreasing energy, giving ^2H/ ^1H and ^3He/ ^1H ratios essentially independent of energy as expected from adiabatic acceleration. The measured ^4He spectrum, however, was essentially flat over this energy interval, and therefore the ^2H/^4He ratio observed at 1 AU is not simply related to the interstellar abundances of...

13. The Quiet Time Spectra of Low Energy Hydrogen and Helium Nuclei - Mewaldt, R. A.; Stone, E. C.; Vogt, R. E.
Measurements of the 1972-1973 quiet time hydrogen and helium spectra from 1.3-40 MeV/nuc are discussed. For both spectra the relative-intensity minimum occurs at lower energies than those reported for earlier years. There is no evidence of a low energy turnup in the He spectrum down to 2.4 MeV/nuc. The spectra indicate that the galactic component dominates down to about 10 MeV; a stable, non-solar He-4 component extends from higher energies down to about 2.4 MeV/nuc. At lower energies the periods of minimum H and He intensity do not coincide, and the relative abundance of H and He at 1.3-2.3 MeV/nuc...

14. A Search for Solar Flare Positrons - Mewaldt, R. A.; Stone, E. C.; Vogt, R. E.
The detection of solar γ-ray line emission and observations of the isotopes ^2H, ^3H and ^3He in solar cosmic rays provide direct evidence for the occurrence of high energy nuclear reactions in solar flare events. Appreciable numbers of other reaction products, including positrons with energies near ~ 1 MeV, should also be produced in such events. We have searched for positrons in the 0.16-1.6 MeV energy interval during 5 "^3He rich" solar particle events observed by the Caltech Electron/Isotope Spectrometers on IMP 7 and 8. Based on calculations of positron and ^3He production at the sun, and using a simplified model of interplanetary propagation, we might expect comparable fluences of positrons...

15. Relation of the Radial Gradient of Cosmic-Ray Protons to the Size of the Solar-Modulation Region - Garrard, T. L.; Stone, E. C.; Vogt, R. E.
The radial intensity-gradient of cosmic-ray protons has been calculated for a range of values of the distance to the boundary of a spherically symmetric solar-modulation region. We find that the radial dependence of the gradients may be described in terms of two characteristic domains of the modulation region: (a) an "inner region" where the gradients are relatively small and constant, and (b), an "outer region"' where the gradients are large and show a strong radial dependence. The magnitude of the gradient in the inner region is small for reasonable values for the physical parameters of the modulation mechanism.

16. Interstellar Electron Spectrum from the Galactic Non-Thermal Radio Emission - Cummings, A. C.; Stone, E. C.; Vogt, R. E.
A range of interstellar electron spectra at energies between 100 MeV and 5 GeV has been derived from an analysis of the observed galactic non-thermal radio spectrum and from consideration of the existing uncertainties in the other relevant physical parameters of the galaxy. We find that for energies larger than ~ 300 MeV the electron spectrum is uncertain to a factor of 4 due to uncertainties in the galactic magnetic field strength and the total line-of-sight emission length. The uncertainty in the electron spectrum increases towards lower energies, exceeding a factor of 50 near 100 MeV, primarily due to uncertainties in the galactic parameters affecting interstellar radio absorption.

17. Measurement of the Cosmic-Ray Be/B Ratio and the Age of Cosmic Rays - Brown, J. W.; Stone, E. C.; Vogt, R. E.
The ratio Be/B depends on whether the confinement time of cosmic rays in the Galaxy is long or short compared to the radioactive half-life of ^(10)Be. We report observations of this ratio which were obtained with a dE/dx-Cerenkov detector launched into a polar orbit on OGO-6 as part of the Caltech Solar and Galactic Cosmic Ray Experiment. Be/B ratios were determined for various rigidity thresholds up to 15 GV. We find no statistically significant rigidity dependence of the ratio, which is 0.41 ± 0.02 when averaged over all observed cutoffs. When averaged over cutoffs ≥1.8 GV, the ratio is 0.43 ± 0.03, which can be compared directly to the ratio...

18. Routes, Processes, and Chance Lowering Causes - Hitchcock, Christopher
[Introduction] Causes often influence their effects via multiple routes. Moderate alcohol consumption can raise the level of HDL ('good') cholesterol, which in tum reduces the risk of heart disease. Unfortunately, moderate alcohol consumption can also increase the level of homocysteine, which in tum increases the risk of heart disease. The net or overall effect of alcohol consumption on heart disease will depend upon both of these routes, and no doubt upon many others as well. This is a familiar fact of life for engineers and policy makers, one that often gives rise to unintended consequences. Suppose, for example, that the American Federal Aviation Administration were to institute new...

19. On the Importance of Causal Taxonomy - Hitchcock, Christopher
Using a standard counterexample to probabilistic theories of causation as an illustration, this chapter argues that there are a number of questions which one might ask about a putative causal relationship: Is it causal at all? What is the direction of the relationship? What is its strength? How does the cause compare with various alternatives? How stable is it under changes in background conditions? What are the pathways responsible for it? Many approaches in philosophy and psychology run these questions together. Together, the answers to these questions can provide a taxonomy of different kinds of causal relationships. By keeping these...

20. Intertemporal Speculation Under Uncertain Future Demand, Experimental Results - Plott, Charles R.; Turocy, Theodore L.
This paper explores a market in which a subset of agents acting independently without direct communication can purchase commodities to carry forward in time in the face of uncertain future demand. The hypothesis that the equilibrating properties of markets will coordinate decentralized decisions to speculate as if all information was public gives no theory about the mechanism through which such information transfer might take place. The results provide general support for the validity of the equilibration suggestion. The mechanisms of information transfer seem to be located in the local nature of the price formation and carry-forward decisions coupled with a...

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