Repository of works by Caltech published authors.
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Mostrando recursos 1 - 20 de 2.897
The descriptive classification of some classes of C∗-algebras - Kechris, Alexander S.
We introduce here a parametrization of separable C*-algebras by a
standard Borel space and study the descriptive complexity of various canonical
classes of C*-algebras in this parametrization. This can be viewed as
providing an analog of the corresponding classification of classes of von Neumann
algebras (acting on a fixed separable Hilbert space) in the Effros Borel
space of von Neumann algebras (see for example Nielsen ). However, in
contrast with the von Neumann case, where most interesting classes (like:
factors, type I, II, III, hyperfinite) turn out to be Borel, in the C*-algebra
case many important classes turn out to be co-analytic but not Borel. This
makes the situation...
Oxygen and hydrogen isotope constraints on the deep circulation of surface waters into zones of hydrothermal metamorphism and melting - Taylor, Hugh P., Jr.
The purpose of this paper is to marshal the evidence
and try to build a case that (1) shallow (1 to 7 km) circulation
of surface waters in the Earth's crust is an extremely
widespread and common phenomenon in areas of igneous
activity and (2) deep (10 to 15 km) circulation of surface
waters can occur in certain favorable geological situations,
particularly in rift zones and areas of extensional tectonics.
It is shown that very large amounts of water may
interact with the rocks in such zones and that this can take
place at temperatures high enough for melting and metamorphism
to occur. Oxygen and hydrogen isotope studies
have proven to...
Discovery of Panguite, a New Ultra-Refractory Titania Mineral in Allende - Ma, Chi; Tschauner, Oliver; Beckett, John R.; Kiefer, Boris; Rossman, George R.; Liu, Wenjun
During our nano-mineralogy investigation
of the Allende meteorite, we identified a new
titania mineral named “panguite” in an ultra-refractory
inclusion within an amoeboid olivine aggregate
(AOA). It has an orthorhombic Pbca structure related
to the Ia3 bixbyite type and a formula unit
(Ti^(4+),Al,Sc,Mg,Zr,Ca,□)_2O_3. We used electron probe
microanalysis (EPMA), high-resolution scanning electron
microscope (SEM), electron backscatter diffraction
(EBSD), synchrotron micro-Laue diffraction with
subsequent energy scans, and micro-Raman analyses
to characterize the composition and structure. Panguite
is not only a new mineral but also a new phase as synthetic
Ia3 (Ti^(4+),Al,Sc,Mg,Zr,Ca,□)_2O_3 is not known.
We report here the type occurrence of this new titania
in nature and discuss implications of this phase for
processes very early in...
Spectroscopy of Micas - Rossman, George R.
This chapter is concerned with spectroscopic studies of micas which address
the origin of their color and pleochroism, the oxidation states and concentrations
of cations, site occupancies and other structural details, thermodynamic
properties, and broader aspects of the chemical-physics of spectroscopic
interactions in general. The field of mica spectroscopy has not previously
been reviewed as a whole, although chapters in Lazarev (1972) and
Farmer (1974) discuss the infrared spectroscopy of layer silicates as a group.
The three primary spectroscopic methods used in this study are Mössbauer
absorption, optical absorption, and infrared absorption. Mössbauer spectra
measure the absorption of gamma rays by ^(57)Fe nuclei. The details of a spectrum
Silica coatings on the 1974 Kilauea flow: new SEM and SIMS results and implications for Mars - Chemtob, S. M.; Rossman, G. R.; Eiler, J. M.; Jolliff, B. L.
Despite the predominately mafic character of martian
surface rocks, silica-rich materials have long been predicted to occur on Mars; recently, those predictions
have been validated. CRISM spectra from numerous regions of Mars have revealed H_2O and OH-bearing phases most consistent with amorphous silica. Additionally, the detection of high-silica materials at Home Plate by MER Spirit implied aqueous alteration and leaching in a volcanic environment . In order to fully understand the environments in which silica-rich materials are formed on Mars, it is useful to study silica in analogous terrestrial settings. We focus on silica and Fe-Ti oxide coatings in the Ka’u Desert...
The Color of Topaz - Rossman, George R.
Topaz, if it is of the ideal composition-free of
minor impurities and free from exposure to
natural (or laboratory) irradiation-would be
colorless because the primary chemical
components of topaz (Al^(3+), Si^(4+), O^(2-), OH^-, and F^-) do not
absorb light in the visible portion of the spectrum. Numerous
examples of natural colorless topaz have been found and
many brown topazes become colorless when exposed to
prolonged sunlight. Topaz also occurs in a variety of colors
ranging through yellow, orange, brown, pink, violet, and
blue. In contrast to that of many other mineral species, most
of the colors of topaz, with the exception of pink, are the
result of either natural or laboratory irradiation.
Isotopic Constraints on Biogeochemical Cycling of Fe - Johnson, Clark M.; Beard, Brian L.; Roden, Eric E.; Newman, Dianne K.; Nealson, Kenneth H.
Cycling of redox-sensitive elements such as Fe is affected by not only ambient Eh-pH conditions, but also by a significant biomass that may derive energy through changes in redox state (e.g., Nealson 1983; Lovely et al. 1987; Myers and Nealson 1988; Ghiorse 1989). The evidence now seems overwhelming that biological processing of redox-sensitive metals is likely to be the rule in surface- and near-surface environments, rather than the exception. The Fe redox cycle of the Earth fundamentally begins with tectonic processes, where “juvenile” crust (high-temperature metamorphic and igneous rocks) that contains Fe which is largely in the divalent state is...
Paleomagnetic results from the Cambrian-Ordovician boundary section at Black Mountain, Georgina Basin, western Queensland, Australia - Ripperdan, Robert L.; Kirschvink, Joseph L.
Zones of alternating magnetic polarity have been identified throughout the
Cambrian-Ordovician sequence at Black Mountain, and can be presumed to record geomagnetic
field reversals during or immediately after deposition. A strong correlation can be made to
polarity zones recognized at Dayangcha, northeastern China, a candidate site for establishment of
the Cambrian-Ordovician boundary Global Stratotype Section and Point. Polarity zones associated
with the Hispidodontus discretus and Hirsutodontus simplex Assemblage-Zones at Black Mountain
are absent at Dayangcha, suggesting hiatuses at these levels in the Dayangcha sequence. Secondary
components preserved in the Black Mountain section may provide temporal constraints on Middle
Paleozoic diagenetic events in the Burke River Structural Belt.
Advances in Shock Compression of Mantle Minerals and Implications - Ahrens, Thomas J.; Asimow, Paul D.; Mosenfelder, Jed L.
Hugoniots of lower mantle mineral compositions are sensitive to the conditions where they cross phase boundaries including both polymorphic phase transitions and partial to complete melting. For SiO_2, the Hugoniot of fused silica passes from stishovite to partial melt (73 GPa, 4600 K) whereas the Hugoniot of crystal quartz passes from CaCi_2 structure to partial melt (116 GPa, 4900 K). For Mg_(2)SiO_4, the forsterite Hugoniot passes from the periclase +MgSiO_3 (perovskite) assemblage to melt before 152 GPa and 4300 K, whereas the wadsleyite Hugoniot transforms first to periclase +MgSiO_3 (post‐perovskite) and then melts at 151 GPa and 4160 K. Shock...
A Fresh Perspective: Learning to Sparsify for Detection in Massive Noisy Sensor Networks - Faulkner, Matthew; Liu, Annie H.; Krause, Andreas
Can one trade sensor quality for quantity? While larger networks with greater sensor density promise to allow us to use
noisier sensors yet measure subtler phenomena, aggregating
data and designing decision rules is challenging. Motivated
by dense, participatory seismic networks, we seek efficient
aggregation methods for event detection. We propose to
perform aggregation by sparsification: roughly, a sparsifying basis is a linear transformation that aggregates measurements from groups of sensors that tend to co-activate,
and each event is observed by only a few groups of sensors.
We show how a simple class of sparsifying bases provably
improves detection with noisy binary sensors, even when
only qualitative information about the...
DNA-directed assembly of multicomponent single-walled carbon nanotube devices - Han, Si-ping; Goddard, William A., III
Single-walled carbon nanotubes (SWNTs) are single layer, graphitic molecular tubes with exceptional
material properties that are well suited to diverse applications in nanotechnology. They are typically
less than 2nm in diameter, but can be centimeters long. They possess very high thermal conductivity,
mechanical strength, stiffness, and chemical stability. Individual nanotubes are metallic or semiconducting,
depending on chirality (Figure 31.1). Semiconducting SWNTs have finite band gap and intrinsic
carrier mobilities on the order of 100,000 cm^2 V^(-1) s^(-16). Both types of SWNTs are 1D quantum wires ENREF_6 with unusual electronic and optoelectronic properties, including ballistic conductance.
Catalytic Enantioselective Alkylation of Prochiral Ketone Enolates - Reeves, Corey M.; Stoltz, Brian M.
The synthesis of stereogenic all-carbon quaternary centers remains a formidable
challenge, notwithstanding the strides made by modem organic chemistry in this
regard. Contemporary advances in enolate alkylation have made it a fundamental
strategy for the construction of C-C bonds. Although methods for the reaction
of a number of enolate types (e.g., ester, ketone, and propionimide) with a variety of
alkylating agents exist, catalytic enantioselective variants of these transformations
are relatively rare. Of the catalytic asymmetric methods available, there have been
few examples of general techniques for the asymmetric alkylation of carbocyclic
systems and still fewer examples that have the capacity to deliver all-carbon
quaternary stereocenters. While the Merck phase...
Magneto-chemical measurements of biochemical compounds with a superconducting magnetometer - Cerdonio, M.; Wang, R. H.; Rossman, G. R.; Mercereau, J. E.
Over the past decade Josephson's predictions1 have been extensively examined
and verified in minute detail by many experimenters. Out of this study has come a
scientific base upon which a new superconducting quantum electronics is being
developed in many laboratories. This paper is a report of the development of a
magnetometer instrument, based on principles of quantum superconductivity, which
is now in routine use in our laboratory for magnetochemical measurements. For this
purpose the high sensitivity of the superconducting magnetic sensor must be matched
by very high standards of reproducibility, reliability, and precision of measurement
over a temperature range from room temperature to below 4.2°K in magnetic fields
Planar Array REDOX Cells and pH Sensors for ISS Water Quality and Microbe Detection - Buehler, Martin G.; Kuhlman, Gregory M.; Myung, Nosang V.; Keymeulen, Didier; Kounaves, Samuel P.; Newman, Dianne; Lies, Douglas
This paper describes results acquired from E-Tongue 2 and E-Tongue 3 which are arrays of planar three-element electrochemical cells and pH sensors. The approach uses ASV (Anodic Stripping Voltammery) to achieve a detection limit, which in the case of Pb, is below one μM which is needed for water quality measurements. The richness of the detectable species is illustrated with Fe where seven species are identified using the Pourbiax diagram. The detection of multiple species is illustrated using Pb and Cu. The apparatus was used to detect the electroactivity of the metabolic-surrogate, PMS (phenazine-methosulphate). Finally, four types of pH sensors...
A new deep-depletion CCD for the red channel of the Palomar Double Spectrograph - Rahmer, Gustavo; Smith, Roger M.; Bui, Khanh; Kirby, Evan; Dekany, Richard; Croner, Ernest; Milburn, Jennifer
The red channel of the Palomar Double Spectrograph (DBSP) on the 200-inch Hale Telescope has been upgraded with a new deep-depletion CCD from LBNL. Its redder response produced a significant increase of the throughput above 550 nm, and its longer dimension more than doubled the spectral coverage. A special Dewar was designed to accommodate a detector mount which includes features to minimize CCD motion due to thermal cycling, in spite of the very simple "picture frame" packaging of the CCD. The new Dewar also includes some novel features to improve the liquid nitrogen hold time while staying within the size...
The Instrumentation Program for the Thirty Meter Telescope - Simard, Luc; Crampton, David; Ellerbroek, Brent; Boyer, Corinne
An overview of the current status of the Thirty Meter Telescope (TMT) instrumentation program is presented. Science cases and operational concepts as well as their links to the instruments are continually revisited and updated through a series of workshops and conferences. Work on the three first-light instruments (WFOS IRIS, and IRMS) has made significant progress, and many groups in TMT partner communities are developing future instrument concepts. Other instrument-related subsystems are also receiving considerable attention given their importance to the scientific end-to-end performance of the Observatory. As an example, we describe aspects of the facility instrument cooling system that are...
GROK-LAB: generating real on-chip knowledge for intra-cluster delays using timing extraction - Gojman, Benjamin; Nalmela, Sirisha; Mehta, Nikil; Howarth, Nicholas; DeHon, André
Timing Extraction identifies the delay of fine-grained components within an FPGA. From these computed delays, the
delay of any path can be calculated. Moreover, a comparison
of the fine-grained delays allows a detailed understanding of
the amount and type of process variation that exists in the
FPGA. To obtain these delays, Timing Extraction measures,
using only resources already available in the FPGA, the delay of a small subset of the total paths in the FPGA. We
apply Timing Extraction to the Logic Array Block (LAB)
on an Altera Cyclone III FPGA to obtain a view of the
delay down to near individual LUT granularity, characterizing components with delays...
Magnetostratigraphy and Clockwise Rotation of the Plio-Pleistocene Mojave River Formation, Central Mojave
Desert, California - Pluhar, Christopher J.; Kirschvink, Joseph L.; Adams, Robert W.
Oriented samples collected for
paleomagnetic analysis from sediments of the
newly-named Mojave River Formation (Nagy
& Murray, 1991, this volume) possess stable
characteristic components of Natural
Remanent Magnetization (NRM). Progressive
demagnetization reveals characteristic
components of both normal and reversed
polarity which are stratigraphically distinct.
The oldest sediments exposed within the field
area are reversely magnetized and were
probably deposited during the early portion of
the Matuyama reversed Chron.
Stratigraphically higher units contain what
appears to be the Olduvai normal Subchron,
as well as a shorter normal zone which
probably is either the Cobb Mountain or
Jaramillo Event. The location of the
Brunhes/Matuyama boundary at one site is
within an alluvial fanglomerate which grades
upward conformably into the lowest unit of
Outcrop Geology of Plio-Pleistocene Strata
of the Confidence Hills,
Southern Death Valley, California - Gomez, F.; Hsieh, J.; Holt, J.; Murray, B.; Kirschvink, J.
The Confidence Hills, Southern Death Valley, California, are composed of Plio-Pleistocene lacustrine beds, evaporite
beds, ashes, playa sediments, alluvial fan and fluvial deposits. The sediments have been divided into 5 mappable units.
From oldest to youngest, they are: the Confidence Hills "formation· (informal) composed of three interfingering
members, and overlying Units A and B which do not exhibit transitional contacts with either underlying units or with
themselves. The Confidence Hills formation includes the lacustrine and playa fine sands, and silts and clays of fluvial
sediments. The lower two members are characterized by the presence of anhydrite. This formation also contains at least
15 volcanic ashes useful...
Magnetostratigraphy of Plio-Pleistocene
Lake Sediments in the Confidence Hills of
southern Death Valley, California - Pluhar, Christopher J.; Holt, John W.; Kirschvink, Joseph L.; Beratan, Kathi K.; Adams, Robert W.
Over 200 meters of continuous playa and lacustrine sediments and volcanic ashes are exposed in the Confidence
Hills of southern Death Valley. Oriented samples from two stream canyons which cut through the sediments possess
stable characteristic components of Natural Remanent Magnetization (NRM). Progressive demagnetization experiments
yield several normal and reversed polarity zones which are stratigraphically distinct, and the characteristic components
pass the reversal test. The presence of the Huckleberry Ridge volcanic ash (c.a. 2 Ma) in one of the reversed polarity
zones provides a dated stratigraphic marker for correlation of the magnetostratigraphy to the magnetic polarity
timescale. The correlation indicates that deposition began before the Reunion...