Repository of works by Caltech published authors.
Type = Book Section
Mostrando recursos 1 - 20 de 3.332
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...
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...
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.
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...
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...
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...
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,...
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...
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...
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....
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...
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...
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...
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
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.
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
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...
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...
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...
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...