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Caltech Authors (91,720 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 40,371

1. On the coherence conjecture of Pappas and Rapoport - Zhu, Xinwen
We prove the (generalized) coherence conjecture proposed by Pappas and Rapoport. As a corollary, one of their theorems, which describes the geometry of the special fibers of the local models for ramified unitary groups, holds unconditionally. Our proof is based on the study of the geometry (in particular, certain line bundles and ℓ-adic sheaves) of the global Schubert varieties, which are the equal characteristic counterparts of the local models.

2. Fracture of Brittle and Quasi-Brittle Engineering Materials - Tandon, S.; Faber, K. T.
The study of fracture of engineering materials involves a number of science and engineering disciplines. Continuum fracture mechanics is deeply rooted in the problem of fracture because it treats the relationship between a crack or inhomogeneity and the stress state in a material. Physics and chemistry are important because they help to explain the reactions between the environment and the crack tip. Finally, materials science is essential in understanding the relations among bond rupture, structure, processing and performance of a material. Fracture of materials can be divided into two broad categories - ductile and brittle fracture. Ductile fracture is associated with appreciable plastic deformation. "Cup and cone" fracture demonstrated...

3. Interpretation of body and Rayleigh waves from NTS to Tucson - Langston, Charles A.; Helmberger, Donald V.
A linear array of eight Caltech portable broad-band seismograph trailers was set out from NTS to near Phoenix, Arizona, for the pre-announced underground nuclear test, OSCURO, on September 21, 1972. Travel-time and amplitude information were used to find an average crustal model by calculating synthetic seismograms using the Cagniard-de Hoop method. Rayleigh waves from other nuclear events at NTS, as recorded at the Tucson WWSSN station, were examined as a control for determining the structure of the top half of the crust. Group-velocity curves were found and synthetic Rayleigh waves calculated for Tucson and Kingman (LRSM). The formations and characteristics...

4. Continuation of a deep borehole stress measurement profile near the San Andreas Fault: 2. Hydraulic fracturing stress measurements at Black Butte, Mojave Desert, California - Stock, J. M.; Healy, J. H.
Hydraulic fracturing stress measurements were obtained in the Black Butte drill hole, 18 km northeast of the San Andreas fault in the Mojave Desert, at depths from 251 to 635 m. In all tests the least and greatest horizontal principal stresses (S_h and S_H, respectively) exceeded the vertical stress (S_ν), indicating a thrust faulting stress regime. A single good-quality hydraulic fracture impression from 309 m depth indicates an S_H direction of N41°E ± 10°. This S_H direction should be interpreted with caution because it is based on only one observation. This orientation is fairly compatible with nearby surface stress measurements...

5. A method for bounding uncertainties in combined plate reconstructions - Molnar, Peter; Stock, Joann M.
We present a method for calculating uncertainties in plate reconstructions that does not describe the uncertainty in terms of uncertainties in pole positions and rotation angles. If a fit of magnetic anomalies of the same age and fracture zones that were active as transform faults at that time can be found, such a reconstruction can be perturbed and degraded by small rotations about each of three orthogonal axes (partial uncertainty poles). If the uncertainty in the reconstruction is a consequence of independent, small, but acceptable, rotations about these axes, then the uncertainties in reconstructed points will be elliptical in shape....

6. Recent erosion in the San Gabriel Mountains - Brown, William M., III; Taylor, Brent D.
Recently the Environmental Quality Laboratory at the California Institute of Technology and the Shore Processes Laboratory at Scripps Institution of Oceanography have undertaken a joint project to study the natural sediment budget in coastal southern California. This budget includes inland erosion which under natural conditions provides sand sized material to nourish the beaches along the shoreline. The San Gabriel Mountains near Los Angeles are an important natural source of sand for beach nourishment. However, the intense urbanization along the base of these mountains have required the advent of extensive flood control structures which significantly reduce the natural transport of sediments from...

7. Hydraulic fracturing stress measurements at Yucca Mountain, Nevada, and relationship to the regional stress field - Stock, J. M.; Healy, J. H.; Hickman, S. H.; Zoback, M. D.
Hydraulic fracturing stress measurements and acoustic borehole televiewer logs were run in holes USW G-1 and USW G-2 at Yucca Mountain as part of the Nevada Nuclear Waste Storage Investigations for the U.S. Department of Energy. Eight tests in the saturated zone, at depths from 646 to 1288 m, yielded values of the least horizontal stress S_h that are considerably lower than the vertical principal stress S_v. In tests for which the greatest horizontal principal stress S_H could be determined, it was found to be less than S_v, indicating a normal faulting stress regime. The borehole televiewer logs showed the...

8. Real-time earthquake hazard assessment in California; the early post-earthquake damage assessment tool and the Caltech-USGS broadcast of earthquakes - Eguchi, Ronald T.; Goltz, James D.; Seligson, Hope A.; Heaton, Thomas H.
A real-time earthquake monitoring system which provides source parameters to user groups through a commercial paging service is now in place in California. A GIS-based system to predict and display near real-time damage and casualty estimates is currently being developed by EQE International under contract with the State of California. These new technologies offer immediate tangible benefits to state and local governments, utilities, lifelines and corporations with facilities or operations at risk. This paper will outline the development of these new technologies, identify the contributions they will make to emergency management and explore some directions these innovative systems may take in the future.

9. Reservoir-induced earthquakes and engineering policy - Allen, Clarence R.
In numerous parts of the world today, including some of the most highly developed countries, many dam designers and operators have tended to close their eyes to the engineering problems posed by reservoir-induced earthquakes. One sometimes hears these kinds of defensive argument: 1) no convincing correlation has yet been demonstrated between earthquakes and reservoirs; 2) since the natural seismicity at a given site is low, the danger of reservoir-inducement is therefore also low; 3) the geology at a given site is different from that at localities where major reservoir-induced events have occurred; 4) only 3 or 4 out of some 11 000 large dams worldwide have experienced significant induced earthquakes, and one should therefore...

10. The Prince William Sound, Alaska, earthquake of 1964 and aftershocks [Book Review] - Hudson, D. E.
This second part of the comprehensive report on the Alaskan earthquake being issued by the U. S. Coast and Geodetic Survey was prepared by practicing engineers for the structural engineering profession. The papers have been assembled by Karl V. Steinbrugge, who has contributed an introduction giving a concise summary of background information on the earthquake engineering aspects of the earthquake.

11. Dynamic Waves in Civil Engineering [Book Review] - Hudson, D. E.
These proceedings of a conference organized by the Society for Earthquake and Civil Engineering Dynamics, which is the British National Section of the International Association for Earthquake Engineering, bring together 19 papers from England, 6 from the United States, 3 from the USSR, and single contributions from Australia, South Africa, and India. About half of the papers are of direct interest to earthquake engineers; of the others, 6 involve mainly ocean waves and their effects on coastal structures, 5 treat of soil and structural dynamics problems of general interest, 2 are concerned with design for wind loads, and the remaining involve background material of a theoretical...

12. Exquisite Sequence Selectivity with Small Conditional RNAs - Sternberg, Jonathan B.; Pierce, Niles A.
Dynamic RNA nanotechnology based on programmable hybridization cascades with small conditional RNAs (scRNAs) offers a promising conceptual framework for engineering programmable conditional regulation in vivo. While single-base substitution (SBS) somatic mutations and single-nucleotide polymorphisms (SNPs) are important markers and drivers of disease, it is unclear whether synthetic RNA signal transducers are sufficiently programmable to accept a cognate RNA input while rejecting single-nucleotide sequence variants. Here, we explore the limits of scRNA programmability, demonstrating isothermal, enzyme-free genotyping of RNA SBS cancer markers and SNPs using scRNAs that execute a conditional hybridization cascade in the presence of a cognate RNA target. Kinetic...

13. Electrocatalytic hydrogen evolution using amorphous tungsten phosphide nanoparticles - McEnaney, Joshua M.; Crompton, J. Chance; Callejas, Juan F.; Popczun, Eric J.; Read, Carlos G.; Lewis, Nathan S.; Schaak, Raymond E.
Amorphous tungsten phosphide (WP), which has been synthesized as colloidal nanoparticles with an average diameter of 3 nm, has been identified as a new electrocatalyst for the hydrogen-evolution reaction (HER) in acidic aqueous solutions. WP/Ti electrodes produced current densities of −10 mA cm^(−2) and −20 mA cm^(−2) at overpotentials of only −120 mV and −140 mV, respectively, in 0.50 M H_2SO_4(aq).

14. THz and mid-IR spectroscopy of interstellar ice analogs: methyl and carboxylic acid groups - Ioppolo, S.; McGuire, B. A.; Allodi, M. A.; Blake, G. A.
A fundamental problem in astrochemistry concerns the synthesis and survival of complex organic molecules (COMs) throughout the process of star and planet formation. While it is generally accepted that most complex molecules and prebiotic species form in the solid phase on icy grain particles, a complete understanding of the formation pathways is still largely lacking. To take full advantage of the enormous number of available THz observations (e.g., Herschel Space Observatory, SOFIA, and ALMA), laboratory analogs must be studied systematically. Here, we present the THz (0.3–7.5 THz; 10–250 cm^(−1)) and mid–IR (400–4000 cm^(−1)) spectra of astrophysically-relevant species that share the...

15. Indicators, Chains, Antichains, Ramsey Property - Sokić, Miodrag
We introduce two Ramsey classes of finite relational structures. The first class contains finite structures of the form (A,(I_i)^n_(i=1),≤,(≾_i)^n_(i=1), where ≤ is a total ordering on A and ≾_i is a linear ordering on the set {ɑ, є A : I_i(ɑ)}. The second class contains structures of the form (ɑ,≤,(i_i)^n_i=1,≾), where (A,≤) is a weak ordering and ≤ is a linear ordering on A such that A is partitioned by {ɑ, є A : I_i(ɑ)} into maximal chains in the partial ordering ≤ and each {ɑ, є A : I_i(ɑ)} is an interval with respect to.

16. Fractal Shear Bands at Elastic-Plastic Transitions in Random Mohr-Coulomb Materials - Li, J.; Ostoja-Starzewski, M.
This paper studies fractal patterns forming at elastic-plastic transitions in soil- and rock-like materials. Taking either friction or cohesion as nonfractal vector random fields with weak noise-to-signal ratios, it is found that the evolving set of plastic grains (i.e., a shear-band system) is always a monotonically growing fractal under increasing macroscopic load in plane strain. Statistical analysis is used to assess the anisotropy of those shear bands. All the macroscopic responses display smooth transitions, but as the randomness vanishes, they turn into a sharp response of an idealized homogeneous material. Parametric study shows that increasing hardening or friction makes the...

17. RNA and dynamic nuclear organization - Rinn, John; Guttman, Mitchell
The human genome consists of more than 2 m of linear DNA, which is packaged into a three-dimensional structure in the nucleus of each cell. To ensure proper cell-type–specific gene regulation, each cell must organize its DNA, RNA, and protein within the nucleus in ways that differ in each cell type. It had long been suspected that RNA itself might be a key organizing factor that shapes this dynamic nuclear floor plan (1), with recent research pointing to a role for nuclear-retained long noncoding RNAs (lncRNAs) in organizing nuclear architecture. Here we provide a perspective on the classical and newly...

18. Large impacts around a solar-analog star in the era of terrestrial planet formation - Meng, Huan Y. A.; Su, Kate Y. L.; Rieke, George H.; Stevenson, David J.; Plavchan, Peter; Rujopakarn, Wiphu; Lisse, Carey M.; Poshyachinda, Saran; Reichart, Daniel E.
The final assembly of terrestrial planets occurs via massive collisions, which can launch copious clouds of dust that are warmed by the star and glow in the infrared. We report the real-time detection of a debris-producing impact in the terrestrial planet zone around a 35-million-year-old solar-analog star. We observed a substantial brightening of the debris disk at a wavelength of 3 to 5 micrometers, followed by a decay over a year, with quasi-periodic modulations of the disk flux. The behavior is consistent with the occurrence of a violent impact that produced vapor out of which a thick cloud of silicate...

19. Industrialized Building in the Soviet Union (A Report of the U.S. Delegation to the USSR) [Book Review] - Housner, G. W.
The report describes building practices in the USSR, particularly the construction of mass-produced apartment buildings. It contains, however, some statistics on the damage to the city of Tashkent by the earthquake of April 26, 1966: "Tashkent, fourth largest of the Soviet cities, demonstrates Russian resolve and the potential for the industrialization of housing. In 1966, an earthquake nearly demolished this city of 1,100,000 in Uzbek Republic. One-third of the total living area was destroyed and another one-sixth was damaged to an extent requiring demolition. The earthquake destroyed 96,000 apartments, 225 nurseries, 181 schools, and 118 medical facilities. Out of this rubble, Tashkent has rebuilt 23,000,000 square feet...

20. The Earth's Density [Book Review] - Anderson, Don L.
Bullen's name is associated with many of the early developments in seismology including the Jeffreys-Bullen travel-time tables and the Bullen density models. His interest in the methodology of scientific inference has always been evident in his papers and continues in this monograph. The Earth's Density is a superb account of the history of a science, starting from ancient determinations of the size and the mass of the Earth up to the modern age of computer inversion.

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