The structure of the crust and distribution of earthquakes in southern California

Nazareth, Julie Jeannine California Institute of Technology 2002 해외박사(DDOD)

The lithologically and tectonically complex crust of southern California and the current broad deformation zone accommodating the relative motion between the Pacific and North American plates, result in significant variations in style, depth distribution, and rate of earthquakes, and thus also in the seismic hazard across southern California. Although the thickness of the seismogenic crust is an important parameter in seismic hazard analysis, it has never been determined systematically for southern California. Seismogenic thickness can be predicted by the depth distribution of the moment release of regional seismicity. The seismogenic thickness of southern California is highly variable, ranging from less than 10 km in the Salton Trough to greater than 25 km at the southwestern edge of the San Joaquin Valley. On average, the seismogenic thickness of southern California is 15.0 km. Seismogenic thickness along the major strike slip systems of southern California can vary significantly along strike. Fault segmentation based upon surface features does not correspond to the variation in seismogenic thickness and thus the potential down-dip width of the fault. A model of the broad scale features of the crust and upper mantle structure of the borderland-continent transition zone adjacent to Los Angeles constrains the crustal thickness and the location and width of the transition zone. The data require the Moho to deepen significantly to the north, dramatically increasing the crustal thickness over a relatively short distance of 20–25 km. The Moho is coherent and laterally continuous beneath the Inner California Borderland and transition zone. The Inner Borderland seems to be modified and thickened oceanic crust, with the oceanic upper mantle intact beneath it. The static stress change triggering model has some validity and can be useful in explaining apparently triggered seismicity within one fault length of a large mainshock. However, because its applicability varies between different sequences, its general application to seismic hazard evaluation requires more refinement and the inclusion of parameters such as tectonic regime, regional stress state, and fault strength.

Field and Laboratory Studies of Atmospheric Organic Aerosol

Coggon, Matthew Mitchell California Institute of Technology 2016 해외박사(DDOD)

This thesis is the culmination of field and laboratory studies aimed at assessing processes that affect the composition and distribution of atmospheric organic aerosol. An emphasis is placed on measurements conducted using compact and high-resolution Aerodyne Aerosol Mass Spectrometers (AMS). The first three chapters summarize results from aircraft campaigns designed to evaluate anthropogenic and biogenic impacts on marine aerosol and clouds off the coast of California. Subsequent chapters describe laboratory studies intended to evaluate gas and particle-phase mechanisms of organic aerosol oxidation. The 2013 Nucleation in California Experiment (NiCE) was a campaign designed to study environments impacted by nucleated and/or freshly formed aerosol particles. Terrestrial biogenic aerosol with > 85% organic mass was observed to reside in the free troposphere above marine stratocumulus. This biogenic organic aerosol (BOA) originated from the Northwestern United States and was transported to the marine atmosphere during periodic cloud-clearing events. Spectra recorded by a cloud condensation nuclei counter demonstrated that BOA is CCN active. BOA enhancements at latitudes north of San Francisco, CA coincided with enhanced cloud water concentrations of organic species such as acetate and formate. Airborne measurements conducted during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) were aimed at evaluating the contribution of ship emissions to the properties of marine aerosol and clouds off the coast of central California. In one study, analysis of organic aerosol mass spectra during periods of enhanced shipping activity yielded unique tracers indicative of cloud-processed ship emissions (m/z 42 and 99). The variation of their organic fraction (f42 and f 99) was found to coincide with periods of heavy (f 42 > 0.15; f99 > 0.04), moderate (0.05 < f42 < 0.15; 0.01 < f99 < 0.04), and negligible (f42 < 0.05; f99 < 0.01) ship influence. Application of these conditions to all measurements conducted during E-PEACE demonstrated that a large fraction of cloud droplet (72%) and dry aerosol mass (12%) sampled in the California coastal study region was heavily or moderately influenced by ship emissions. Another study investigated the chemical and physical evolution of a controlled organic plume emitted from the R/V Point Sur. Under sunny conditions, nucleated particles composed of oxidized organic compounds contributed nearly an order of magnitude more cloud condensation nuclei (CCN) than less oxidized particles formed under cloudy conditions. The processing time necessary for particles to become CCN active was short ( 4 hr). Laboratory chamber experiments were also conducted to evaluate particle-phase processes influencing aerosol phase and composition. In one study, ammonium sulfate seed was coated with a layer of secondary organic aerosol (SOA) from toluene oxidation followed by a layer of SOA from &agr;-pinene oxidation. The system exhibited different evaporative properties than ammonium sulfate seed initially coated with &agr;-pinene SOA followed by a layer of toluene SOA. This behavior is consistent with a shell-and-core model and suggests limited mixing among different SOA types. Another study investigated the reactive uptake of isoprene epoxy diols (IEPOX) onto non-acidified aerosol. It was demonstrated that particle acidity has limited influence on organic aerosol formation onto ammonium sulfate seed, and that the chemical system is limited by the availability of nucleophiles such as sulfate. Flow tube experiments were conducted to examine the role of iron in the reactive uptake and chemical oxidation of glycolaldehyde. Aerosol particles doped with iron and hydrogen peroxide were mixed with gas-phase glycolaldehyde and photochemically aged in a custom-built flow reactor. Compared to particles free of iron, iron-doped aerosols significantly enhanced the oxygen to carbon (O/C) ratio of accumulated organic mass. The primary oxidation mechanism is suggested to be a combination of Fenton and photo-Fenton reactions which enhance particle-phase OH radical concentrations.

Part I. Tectonic evolution of the northern Gulf of California, Mexico, deduced from conjugate rifted margins of the Upper Delfin basin. Part II. Active folding and seismic hazard in central Los Angeles, California

Oskin, Michael Eugene California Institute of Technology 2002 해외박사(DDOD)

Part I of this thesis addresses the tectonic evolution of the Pacific-North America plate boundary through northwest Mexico and its implications for rifting processes. Offset ignimbrites support 255 ± 10 km of opening across the Upper Delfín basin of the northern Gulf of California. Additional deformation from the continental margins supports 296 ± 17 km total plate boundary displacement between coastal Sonora and the Main Gulf Escarpment in Baja California, of which at least 276 ± 13 km occurred since ∼6 Ma. This strain history requires that the plate boundary localized into the northern Gulf of California during latest Miocene time. Only a narrow width of upper continental crust foundered into the Upper Delfín basin, such that most of the crust between Isla Tiburón and Baja California must be new transitional oceanic crust and possibly lower continental crust contributed by inflow from the rift flanks. Extension of the margins of the Upper and Lower Delfín basins is <40% in most places, though the whole crustal column may have been thinned by a factor of two, further supporting that lower crustal flow has operated here. Opening of the Upper Delfín basin was accompanied by a steady or increased strain rate on its continental margins, contrary to the expected rheology of a narrow continental rift. Reevaluation of a critical deposit of marine rocks on Isla Tiburón indicates that initial marine incursion in the northern Gulf of California also occurred during latest Miocene time. Together, these records suggest that opening of the Upper Delfín basin was an abrupt event, accompanied by a localized zone of intense extension, marine incursion, and a rapid increase in strain rate. Continental rupture in the Upper Delfín basin does not appear to have been a response to crustal weakening by intracontinental extension, but rather may have resulted from a significant increase in strain rate, brought on by a change in boundary forces. Part II of this thesis develops methods to estimate seismic hazard from blind reverse faults by analysis of fault-related folding of Late Quaternary strata, with application to the Elysian Park anticline of Los Angeles, California.

Integrated parylene LC-ESI on a chip

Xie, Jun California Institute of Technology 2005 해외박사(DDOD)

In this thesis, several microfluidic devices will be introduced to demonstrate the integration capability of a multilayer parylene surface micromachining technology. Due to its flexibility and versatility, various devices have been developed and integrated onto a single ship. Based on the technology, on-chip LC-ESI was successfully demonstrated. Based on the technology, an electrostatically actuated micro peristaltic pump has been developed. An AC actuation voltage combined with a peristaltic actuation was used to demonstrate fluid pumping. A reasonable flow rate and pumping pressure were achieved. The pump dynamics and performance were then addressed further by an analysis based on a lumped-parameter model of the system. Based on the same technology, an entirely surface micromachined electrostatically actuated valve has been demonstrated. A thermal flow sensor was integrated with the valve to be used for feedback control. Two modes, actuation voltage adjustment and PWM were investigated in characterizing the valve to control air flow. The testing results show that PWM has better linearity and performance. Three types of capacitive fluidic sensors were demonstrated in several microfluidic applications. These include sensors for fluid pressure, flow rate, volume, and composition measurement. The sensors showed great promise for microfluidic applications because of their high sensitivity and easy integration capabilities. The integration of these sensors with abovementioned devices was achieved. A novel electrochemical pumping system for on-chip LC gradient generation was demonstrated. This pump was able to deliver significant flow rates under high back pressures that are sufficient for many LC applications. On-chip gradient formation with integrated electrospray ionization was demonstrated. Finally, a complete LC-ESI system was integrated in a chip format. Typical nano-LC reversed-phase gradient elution was demonstrated using on-chip electrolysis pump. Separated analytes from on-chip column were then sprayed into MS for analysis through an integrated ESI-nozzle. Separation results are comparable to those of commercial system. Peptide identification performance using the LC-ESI chip with MS was also very close to those achieved by the commercial system.

Electrical and Optical Interconnects for High-Performance Computing

Honarvar Nazari, Meisam California Institute of Technology 2013 해외박사(DDOD)

Technology scaling has enabled drastic growth in the computational and storage capacity of integrated circuits (ICs). This constant growth drives an increasing demand for high-bandwidth communication between and within ICs. In this dissertation we focus on low-power solutions that address this demand. We divide communication links into three subcategories depending on the communication distance. Each category has a different set of challenges and requirements and is affected by CMOS technology scaling in a different manner. We start with short-range chip-to-chip links for board-level communication. Next we will discuss board-to-board links, which demand a longer communication range. Finally on-chip links with communication ranges of a few millimeters are discussed. Electrical signaling is a natural choice for chip-to-chip communication due to efficient integration and low cost. IO data rates have increased to the point where electrical signaling is now limited by the channel bandwidth. In order to achieve multi-Gb/s data rates, complex designs that equalize the channel are necessary. In addition, a high level of parallelism is central to sustaining bandwidth growth. Decision feedback equalization (DFE) is one of the most commonly employed techniques to overcome the limited bandwidth problem of the electrical channels. A linear and low-power summer is the central block of a DFE. Conventional approaches employ current-mode techniques to implement the summer, which require high power consumption. In order to achieve low-power operation we propose performing the summation in the charge domain. This approach enables a low-power and compact realization of the DFE as well as crosstalk cancellation. A prototype receiver was fabricated in 45nm SOI CMOS to validate the functionality of the proposed technique and was tested over channels with different levels of loss and coupling. Measurement results show that the receiver can equalize channels with maximum 21dB loss while consuming about 7.5mW from a 1.2V supply. We also introduce a compact, low-power transmitter employing passive equalization. The efficacy of the proposed technique is demonstrated through implementation of a prototype in 65nm CMOS. The design achieves up to 20Gb/s data rate while consuming less than 10mW. An alternative to electrical signaling is to employ optical signaling for chip-to-chip interconnections, which offers low channel loss and cross-talk while providing high communication bandwidth. In this work we demonstrate the possibility of building compact and low-power optical receivers. A novel RC front-end is proposed that combines dynamic offset modulation and double-sampling techniques to eliminate the need for a short time constant at the input of the receiver. Unlike conventional designs, this receiver does not require a high-gain stage that runs at the data rate, making it suitable for low-power implementations. In addition, it allows time-division multiplexing to support very high data rates. A prototype was implemented in 65nm CMOS and achieved up to 24Gb/s with less than 0.4pJ/b power efficiency per channel. As the proposed design mainly employs digital blocks, it benefits greatly from technology scaling in terms of power and area saving. As the technology scales, the number of transistors on the chip grows. This necessitates a corresponding increase in the bandwidth of the on-chip wires. In this dissertation, we take a close look at wire scaling and investigate its effect on wire performance metrics. We explore a novel on-chip communication link based on a double-sampling architecture and dynamic offset modulation technique that enables low power consumption and high data rates while achieving high bandwidth density in 28nm CMOS technology. The functionality of the link is demonstrated using different length minimum-pitch on-chip wires. Measurement results show that the link achieves up to 20Gb/s of data rate (12.5Gb/s/microm) with better than 136fJ/b of power efficiency.

Spectral-element simulations of three-dimensional seismic wave propagation and applications to source and structural inversions

Liu, Qinya California Institute of Technology 2006 해외박사(DDOD)

This thesis presents a concise introduction to the spectral-element method and its applications to the simulation of seismic wave propagation in 3-D earth models. The spectral-element method is implemented in the regional scale for a 3-D integrated southern California velocity model. Significantly better waveform fits are achieved for the 3-D synthetics calculated compare to the 1-D synthetics generated from the 1-D standard southern California model, especially for many basin stations where strong amplifications are observed due to the very low wave-speed sediments. A hypothetical earthquake rupturing from northeast to southwest at the southern end of the San Andreas fault is simulated to improve our understanding of the seismic hazards in the Salton Trough region. With the improved 3-D Green's function, we perform source inversions for both the source mechanisms and event depths of Mw ≥ 3.5 earthquakes in southern California. The inversion results generally agree well with the results obtained by other traditional methods, but with significantly more stations used in the inversions. Time shifts are generally required to align the data and the synthetics, which provides a great dataset for the improvement of the 3-D velocity models in southern California. We use the adjoint method to formulate the tomographic inverse problem based upon a 3-D initial model. We calculate the sensitivity kernels, a key component of the tomographic inversion, that relate the perturbations of observations to the perturbations of the model parameters. These kernels are constructed by the interaction of the regular forward wavefield and the adjoint wavefield generated by putting the time-reversed signals at the receivers as simultaneous adjoint sources. We compute the travel-time sensitivity kernels for typical phases in both regional and global problems for educational purposes, and outline the procedures of applying the conjugate-gradient method to solve both source and structural inversion problems.

Temperature-controlled microchip liquid chromatography system

Shih, Victor Chi-Yuan California Institute of Technology 2006 해외박사(DDOD)

High-performance liquid chromatography (HPLC) is one of the most important analytical tools heavily used in the fields of chemistry, biotechnology, pharmaceutics, and the food industry. The power of liquid chromatography comes from its ability to achieve molecular separation with extremely high efficiency and its great flexibility of incorporating versatile sensors for detecting a broad range of analytes. In the past decades, great efforts have been put into liquid chromatography instrumentation and methods, aiming to further improve separation efficiency, sensitivity, repeatability, throughput, and costs. The contribution of this thesis is to illustrate with real examples the great potential of MEMS microchip liquid chromatography systems with on-chip temperature control for replacing and improving the conventional desktop HPLC systems. This thesis is composed of seven chapters. Chapter 1 gives an introduction to MEMS technology and its application in making lab-on-a-chip systems. Chapter 2 describes the theoretical background and the evolution of HPLC technology. Chapter 3 demonstrates how to use state-of-the-art MEMS technology to make high-pressure microfluidic channels, which will be used for constructing microchip HPLC systems later. Chapter 4 describes a temperature-controlled microchip HPLC system that uses a temporal temperature gradient to achieve analyte elution. Separation of amino acids and low density lipoproteins was successfully demonstrated using the proposed system. Chapter 5 describes a novel embedded HPLC system, which demonstrated a record high pressure capacity (> 1000 psi) among microchip HPLC systems. High quality separation results of trace-level daunorubicin and doxorubicin were obtained using the proposed system and laser-induced fluorescence detection. A novel C4D sensor together with the RISE sensitivity enhancement method was proposed and investigated for the first time for microchip HPLC analyte detection. Chapter 6 describes the first work to pack 30 nm gold nanoparticles into the HPLC separation column as the stationary phase with the assistance of in-situ molecular self-assembly between nanoparticles and thiolated molecules. Preliminary results demonstrated the possibility of building fully filled nanoparticle HPLC columns for extremely high separation efficiency application. Chapter 7 then gives the conclusions of this thesis.

Experimental and computational studies of secondary organic aerosol formation

Griffin, Robert John California Institute of Technology 2000 해외박사(DDOD)

Organic species are important constituents of tropospheric particulate matter in remote, rural, and urban areas. Such aerosol can be primary (emitted in the particle phase as solids or liquids) or secondary (formed <italic> in situ</italic> as condensable vapors) in nature. Secondary organic aerosol (SOA) is formed when products resulting from the gas-phase oxidation of a parent organic species partition to the particle phase. This partitioning can occur via condensation onto existing inorganic aerosol (heterogeneous-heteromolecular nucleation), absorption into an existing organic aerosol, dissolution to the aerosol aqueous phase, or homogeneous-heteromolecular nucleation. SOA yield is defined as the amount of SOA formed per the amount of a parent organic species that is oxidized. This yield depends functionally on stoichiometric and partitioning coefficients for each of the oxidation products formed and the total amount of organic aerosol mass available to act as absorptive media. Appropriate yield parameters are developed for a series of parent organics using smog chamber experiments. The effects of parent organic structure and the oxidizing species on SOA yield are also examined during the smog chamber experiments. Such yield parameters are used to model SOA formation from the oxidation of biogenic organic species on a global and annual scale. Yield parameters can also be used to define a new concept, the incremental aerosol reactivity for parent organic species, which is a convenient way of ranking parent organics in terms of their SOA-forming potentials. Efforts to improve the simulation of SOA formation in the California Institute of Technology three-dimensional air quality model are also described. The Caltech Atmospheric Chemistry Mechanism was designed to predict concentrations of the highly functionalized secondary organic oxidation products capable of leading to SOA. A module that treats formation of SOA thermodynamically is used to predict the distribution of these products between the gas- and aerosol-phases. The new mechanism and thermodynamic module will used to simulate a smog episode that occurred in 1993 in the South Coast Air Basin of California.

Geochemistry of uranium at mineral-water interfaces: Rates of sorption-desorption and dissolution-precipitation reactions

Giammar, Daniel Edward California Institute of Technology 2001 해외박사(DDOD)

The extraction and processing of uranium for use in the nuclear weapons program and in commercial nuclear energy has led to extensive contamination of the environment. Migration of uranium is also a concern for the proposed long-term nuclear waste disposal in geologic repositories. Reactions occurring at mineral surfaces significantly affect the mobility of uranium in the environment. Both the equilibrium and kinetics of reactions at mineral surfaces must be understood in order to predict the extent of reactions on time scales pertinent to human exposure. Such information is needed to establish input parameters for reactive transport models and to design remediation technologies. Rates of uranium sorption on mineral surfaces and the dissolution of uranium-containing minerals have been investigated. Rates of sorption onto and desorption from goethite, an important environmental sorbent, were determined by measuring the responses of goethite suspensions (pre-equilibrated with or without uranium) to perturbations of the solution chemistry. Dissolution rates were measured for a set of laboratory-synthesized minerals: the uranyl oxide hydrate schoepite, the uranyl silicate soddyite, and a uranyl phosphate phase. These minerals have been observed in contaminated environments and are produced during the corrosion of spent nuclear fuel. Mineral dissolution and transformation were monitored in batch reactors, while dissolution rates were quantified in flow-through reactors. In both sorption and dissolution-precipitation studies, measurements of bulk solution chemistry were integrated with solid phase characterization. While sorption processes were rapid, dissolution and surface-precipitation reactions occurred more slowly. Adsorption and desorption reactions of uranium onto or from goethite reached greater than 50% completion within minutes and completion on a time-scale of hours. In some uranium-goethite suspensions, a meta-stable sorption state persisted for as long as three weeks before a schoepite-like phase precipitated. Dissolution reactions proceeded at time-scales of hours for schoepite and days to weeks for soddyite and the uranyl phosphate. Common groundwater cations affected dissolution rates and, in several cases, resulted in the precipitation of uranium in secondary phases. In several schoepite and soddyite batch dissolution experiments, uranium ultimately reprecipitated in sodium or cesium uranyl oxide hydrate phases which subsequently controlled the dissolved uranium concentration.

Understanding an economic dilemma: Essays on common property resources

Casari, Marco California Institute of Technology 2002 해외박사(DDOD)

There are many economic environments in which individual incentives do not generate enough group cooperation. This dissertation investigates, from three distinct perspectives, one such social dilemma—the use of a common property resource—and a special class of solutions, namely self-governing institutions. In the first essay, game theory and the economics of property rights are applied to a field case study concerning the collective use of renewable resources. For six centuries, many communities in the Italian Alps managed their common forests and pastures through contracts negotiated and enforced among themselves (<italic>Carte di Regola</italic>). This legal solution to the Tragedy of the Commons is compared with the potential for informal cooperation through repeated interaction (Folk theorem). The two solutions are found to often be complementary rather than alternative. In the second essay, a simplified version of the decentralized monitoring and sanctioning mechanism devised historically to enforce regulations on the commons is studied experimentally. Individual users were allowed to inspect others at their own cost and to impose a predetermined fine when a free rider was discovered. The fine was paid to the inspector. We find that; first, this mechanism considerably improves efficiency of resource use, and, second, that the model of other-regarding preferences with altruism and spite better explains the data than the classical model with identical, selfish agents. Finally, an alternative explanation of the above experimental data is given by using selfish agents with bounded rationality. Simulations are carried out using a version of genetic algorithms with memory sets. We find that most aspects of the data with human agents are replicated, and new predictions are made. Interestingly, in this computational study, less sophisticated adaptive agents exhibit a higher degree of individual heterogeneity. In addition, the impact of the process that generates new ideas is explored by comparing the conventional uniform binary mutation with two other alternatives.