Repository of works by Caltech published authors.
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Extinction of the dinosaurs: A 1982 understanding - Schopf, Thomas J. M.
The objective record appears to be that the dinosaur fauna of the latest Maastrichtian (i.e., latest Cretaceous) was chiefly (and perhaps exclusively) restricted to the Western Interior Seaway of the United States and southern Canada and included fewer than 20 species distributed among approximately 15 genera and 10 families. In the late Maastrichtian, as has been known for many years, sea level went down by 150 to 200 m in the western interior. The interior seaway (along which the dinosaurs were living) dried up and seasonality increased and habitable area was reduced as widespread flood plains yielded to uplifted, restricted...
The interaction of the Cretaceous/Tertiary Extinction Bolide with the atmosphere, ocean, and solid Earth - O'Keefe, John D.; Ahrens, Thomas J.
The mechanics of large-scale (~10-km diameter) asteroidal, cometary, and meteoroid swarm impact onto a silicate Earth covered by water and a gas layer (atmosphere) demonstrate that only ~ 15% to ~ 5% of the energy of 15 to 45 km/s bolides is taken up directly during the passage through the ocean and atmosphere, respectively. Upon impact with the Earth, ~ 10 to 10^2 times the bolide mass of water or rock can be ejected to the stratosphere: however, only ~0.1 bolide masses is in < 1 μm particles. The vaporized, melted, and (< 1 mm) solid ejecta transfer up to...
Tectonic development of Cordilleran mid-Paleozoic volcano-plutonic complexes; Evidence for convergent margin tectonism - Rubin, Charles M.; Miller, M. Meghan; Smith, George M.
Devonian and Lower Mississippian volcano-plutonic complexes and related basinal strata that extend from California to British Columbia lie outboard of coeval North American shelf rocks. Remarkable similarities between these complexes indicate that they form the remnants of a mid-Paleozoic east Pacific fringing arc system. Arc basement was composite. It is characterized in part by high initial Sr ratios, radiogenic Pb, and −ɛ_(Nd) values, and in part by low initial Sr ratios, various initial Pb ratios, and +ɛ_(Nd) values. These distinctive isotopic signatures, together with the presence of Proterozoic average ages for detrital zircon in ultimately continent-derived sedimentary rocks and Proterozoic...
Toward Monodisperse Poly(γ-benzyl α,L-glutamate): Uniform, Polar, Molecular Rods - Zhang, Guanghui; Fournier, Maurille J.; Mason, Thomas L.; Tirrell, David A.
Poly(γ-benzyl α,L-glutamate) (PBLG) has been widely used in studies of the physics of rod-like polymer chains. The helical structure of PBLG gives rise to considerable chain stiffness, such that the persistence length of the chain is on the order of 70 nm in helicogenic solvents. This feature, coupled with the ease of synthesis and good solubility of the polymer has made PBLG the system of choice for the study of both isotropic and liquid crystalline solutions of rod-like macromolecules.
Comments on the Role of Molecular Genetics in Polymer Materials Science - Fournier, Maurille J.; Mason, Thomas L.; Tirrell, David A.
The most fundamental goal of the synthetic chemist is control of molecular architecture. With respect to small molecules (i.e., those of molecular weight less than a few thousand), this means absolute control of chemical connectivity and stereochemistry – complete specification of molecular structure. But in macromolecular chemistry, controlled architecture has meant something quite different. Because polymerizations are in general statistical processes, conventional polymeric materials are characterized by substantial heterogeneity in chain length, sequence and stereochemistry. Control is exercised in a statistical sense only, and considerable skill is required to control even the average properties of the chain population and the...
Device Modeling of Dye-Sensitized Solar Cells - Bisquert, Juan; Marcus, Rudolph A.
We review the concepts and methods of modeling of the dye-sensitized solar cell, starting from fundamental electron transfer theory, and using phenomenological transport-conservation equations. The models revised here are aimed at describing the components of the current–voltage curve of the solar cell, based on small perturbation experimental methods, and to such an end, a range of phenomena occurring in the nanoparticulate electron transport materials, and at interfaces, are covered. Disorder plays a major role in the definition of kinetic parameters, and we introduce single particle as well as collective function definitions of diffusion coefficient and electron lifetime. Based on these...
In Vivo Synthesis and Structural Analysis of Alanylglycine-Rich Artificial Proteins - Cantor, Eric J.; Creel, Howard S.; Deguchi, Yoshikuni; Dougherty, Michael J.; Kothakota, Srinivas; Krejchi, Mark T.; Matsuki, Kunio; McGrath, Kevin P.; Parkhe, Ajay D.; Atkins, Edward D. T.; Fournier, Maurille J.; Mason, Thomas L.; Tirrell, David A.
A series of 22 alanylglycine-rich artificial proteins has been prepared by bacterial expression of the corresponding synthetic genes. These polymers have been isolated and purified, and subjected to structural analysis by gel electrophoresis, mass spectrometry, x-ray scattering, and vibrational and NMR spectroscopy. Strategies have been developed for the in vivo synthesis of artificial proteins containing non-natural amino acids.
Magnetic Cataclysmic Variables Discovered in the Palomar Transient Factory - Margon, Bruce; Levitan, David; Prince, Thomas A.; Hallinan, Gregg
The Palomar Transient Factory proves to be a prolific source of Magnetic Cataclysmic Variables, selected by their distinctive photometric variability, and followed up spectroscopically. Here, we present six new candidate systems, together with preliminary photometric periods and spectra.
Amorphization and recrystallization in MeV ion implanted InP crystals - Xiong, Fulin; Nieh, C. W.; Jamieson, D. N.; Vreeland, T., Jr.; Tombrello, T. A.
A comprehensive study of MeV-^(15)N-ion-implanted InP by a variety of analytical techniques has revealed the physical processes involved in MeV ion implantation into III-V compound semiconductors as well as the influence of post-implantation annealing. It provides a coherent picture of implant distribution, structural transition, crystalline damage, and lattice strain in InP crystals induced by ion implantation and thermal annealing. The experimental results from the different measurements are summarized in this report. Mechanisms of amorphization by implantation and recrystallization through annealing in MeV-ion-implanted InP are proposed and discussed in light of the results obtained.
Solar Eruptions and Energetic Particles: An Introduction - Gopalswamy, N.; Mewaldt, R. A.; Torsti, J.
This introductory article highlights current issues concerning two related
phenomena involving mass emission from the Sun: solar eruptions and solar
energetic particles. A brief outline of the chapters is provided indicating how the current issues are addressed in the monograph. The sections in this introduction roughly group the chapters dealing with coronal mass ejections (CMEs), solar energetic particles (SEPs), shocks, and space weather. The concluding remarks include a brief summary of outstanding issues that drive current and future research on CMEs and SEPs.
A 4-to-11GHz Injection-Locked Quarter-Rate Clocking for an Adaptive 153fJ/b Optical Receiver in 28nm FDSOI CMOS - Raj, Mayank; Saeedi, Saman; Emami, Azita
Modern SoC systems impose stringent requirements on on-chip clock
generation and distribution. Ring-oscillator (RO) based injection-locked (IL)
clocking has been used in the past  to provide a low-power, low-area and
low-jitter solution. Ring-based injection-locked oscillators (ILO) can also be
used to generate quadrature phases from a reference clock  without
frequency division, which is desirable for half-rate and quarter-rate CDR.
However, ILO inherently has a small locking range  making it less suitable for
wideband applications. In addition, drift in the free-running frequency due to PVT
variations may lead to poor jitter performance and locking failures . Adding a
PLL to an ILO provides frequency tracking. However, PLL-aided...
The Source Material for Large Solar Energetic Particle Events - Mewaldt, R. A.; Cohen, C. M. S.; Mason, G. M.
We review evidence regarding the origin of material accelerated in large, gradual solar energetic particle (SEP) events. According to the two-class paradigm in place at the start of solar cycle 23, impulsive SEP events accelerate heated flare material, while gradual SEP events are accelerated out of the solar wind by shocks driven by fast coronal mass ejections (CMEs). However, new data from solar cycle 23 has shown that the energetic ions in gradual events often include composition signatures associated with impulsive events, including enrichments in ^3He, heavy elements such as Fe, and ionic charge states indicative of~ 10 MK temperatures....
Localized distributed state feedback control with communication delays - Wang, Yuh-Shyang; Matni, Nikolai; You, Seungil; Doyle, John C.
This paper introduces the notion of localizable distributed systems. These are systems for which a distributed controller exists that limits the effect of each disturbance to some local subset of the entire plant, akin to spatio-temporal dead-beat control. We characterize distributed systems for which a localizing state-feedback controller exists in terms of the feasibility of a set of linear equations. We then show that when a feasible solution exists, it can be found in a distributed way, and used for the localized synthesis and implementation of controllers that lead to the desired closed loop response. In particular, by allowing controllers...
Semidefinite Relaxations for Stochastic Optimal Control Policies - Horowitz, Matanya B.; Burdick, Joel W.
Recent results in the study of the Hamilton Jacobi Bellman (HJB) equation have led to the discovery of a formulation of the value function as a linear Partial Differential Equation (PDE) for stochastic nonlinear systems with a mild constraint on their disturbances. This has yielded promising directions for research in the planning and control of nonlinear systems. This work proposes a new method obtaining approximate solutions to these linear stochastic optimal control (SOC) problems. A candidate polynomial with variable coefficients is proposed as the solution to the SOC problem. A Sum of Squares (SOS) relaxation is then taken to the...
Collaborative System Identification via Parameter Consensus - Papusha, Ivan; Lavretsky, Eugene; Murray, Richard M.
Classical schemes in system identification and adaptive control often rely on persistence of excitation to guarantee parameter convergence, which may be difficult to achieve with a single agent and a single input. Inspired by consensus systems, we extend classical parameter adaptation to the multi agent setting by combining an adaptive gradient law with consensus dynamics. The gradient law represents the main learning signal, while consensus dynamics attract each agent's parameter estimates toward those of its neighbors. We show that the resulting decentralized online parameter estimator can be used to identify the true parameters of all agents, even if no single...
A Fast Linear Consensus Protocol on an Asymmetric Directed Graph - You, Seungil
In this paper, we generalize a fast linear consensus protocol design (Fastest Distributed Linear Averaging) from symmetric undirected graphs to asymmetric directed graphs. This design problem can be cast as a non-convex optimization. We propose a procedure to approximately solve this optimization problem using a sequence of semidefinite programs. Our procedure is guaranteed to generate a consensus protocol for a strongly connected graph that shows a faster convergence compared to the protocols from existing algorithms in our simulation.