Recursos de colección

Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

Group = Resnick Institute

Mostrando recursos 1 - 14 de 14

  1. Analysis of Surface Materials by the Curiosity Mars Rover: Introduction

    Grotzinger, John P.
    The 6 August 2012 arrival of the Curiosity Rover on the surface of Mars delivered the most technically advanced geochemistry laboratory ever sent to the surface of another planet. Its 10 instruments (1)* were commissioned for operations and were tested on a diverse set of materials, including rocks, soils, and the atmosphere, during the first 100 martian days (sols) of the mission. The five articles presented in full in the online edition of Science (, with abstracts in print (pp. 1476–1477), describe the mission’s initial results, in which Curiosity’s full laboratory capability was used.

  2. Branch Flow Model: Relaxations and Convexification—Part II

    Farivar, Masoud; Low, Steven H.
    We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact but the angle relaxation may not be exact,...

  3. Swing dynamics as primal-dual algorithm for optimal load control

    Zhao, Changhong; Topcu, Ufuk; Low, Steven
    In electricity transmission networks, loads can provide flexible, fast responsive, and decentralized sources for frequency regulation and generation-demand balancing, complementary to generation control. We consider an optimal load control (OLC) problem in a transmission network, when a disturbance in generation occurs on an arbitrary subset of the buses. In OLC, the frequency-insensitive loads are reduced (or increased) in real-time in a way that balances the generation shortfall (or surplus), resynchronizes the bus frequencies, and minimizes the aggregate disutility of load control. We propose a frequency-based load control mechanism and show that the swing dynamics of the network, together with the...

  4. Exact Convex Relaxation of OPF for Radial Networks using Branch Flow Model

    Li, Na; Chen, Lijun; Low, Steven H.
    The optimal power flow (OPF) problem is generally nonconvex. Recently a second-order cone relaxation for OPF has been proposed using the branch flow model. In this paper, we provide sufficient conditions under which the relaxation is exact, and demonstrate that these conditions hold for a wide class of practical power distribution systems.

  5. Chemical Stability of (Ag,Cu)_2Se: a Historical Overview

    Brown, David R.; Day, Tristan; Caillat, Thierry; Snyder, G. Jeffrey
    Recent work on Cu_(2−x) Se has caused strong interest in this material due to its high reported peak zT (1.5) and the reduction of thermal conductivity through the mechanism of liquid-like suppression of heat capacity. In the 1960s, 3M patented Cu_(1.97)Ag_(0.03)Se as “TPM-217.” Over the following decade it was tested and developed by the 3M Corporation, at the National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory, Teledyne Energy Systems, and the General Atomics Corporation for use as a next-generation thermoelectric material. During these tests, extreme problems with material loss through Se vaporization and chemical reactions between the material and...

  6. Some Problems in Demand Side Management

    Gan, Lingwen; Jiang, Libin; Low, Steven; Topcu, Ufuk; Zhao, Changhong
    We present a sample of problems in demand side management in future power systems and illustrate how they can be solved in a distributed manner using local information. First, we consider a set of users served by a single load-serving entity (LSE). The LSE procures capacity a day ahead. When random renewable energy is realized at delivery time, it manages user load through real-time demand response and purchases balancing power on the spot market to meet the aggregate demand. Hence optimal supply procurement by the LSE and the consumption decisions by the users must be coordinated over two timescales, a day ahead and in real time, in the presence of...

  7. Demand response in radial distribution networks: Distributed algorithm

    Li, Na; Chen, Lijun; Low, Steven H.
    Demand response has recently become a topic of active research. Most of work however considers only the balance between aggregate load and supply, and abstracts away the underlying power network. In this paper, we study demand response in a radial distribution network, by formulating it as an optimal power flow problem that maximizes the aggregate user utilities and minimizes the supply cost and the power line losses, subject to the power flow constraints and operating constraints. We propose a fully distributed algorithm for the users to coordinate their demand response decisions through local communication with their neighbors so as to...

  8. A diverse set of family 48 bacterial glycoside hydrolase cellulases created by structure-guided recombination

    Smith, Matthew A.; Rentmeister, Andrea; Snow, Christopher D.; Wu, Timothy; Farrow, Mary F.; Mingardon, Florence; Arnold, Frances H.
    Sequence diversity within a family of functional enzymes provides a platform for elucidating structure–function relationships and for protein engineering to improve properties important for applications. Access to nature's vast sequence diversity is often limited by the fact that only a few enzymes have been characterized in a given family. Here, we recombined the catalytic domains of three glycoside hydrolase family 48 bacterial cellulases (Cel48; EC – Clostridium cellulolyticum CelF, Clostridium stercorarium CelY, and Clostridium thermocellum CelS – to create a diverse library of Cel48 enzymes with an average of 106 mutations from the closest native enzyme. Within this set,...

  9. Precisely Tunable Photonic Crystals From Rapidly Self-Assembling Brush Block Copolymer Blends

    Miyake, Garret M.; Piunova, Victoria A.; Weitekamp, Raymond A.; Grubbs, Robert H.
    Colorful: Enabled by their reduced capacity for chain entanglement, high-molecular-weight brush block copolymers can rapidly self-assemble to photonic crystals. The blending of two polymers of different molecular weight can predictably modulate the sizes of the polymer domains, giving rise to a facile means of precision tuning of these photonic-band-gap materials.

  10. Evaluation of the Thermodynamic Properties of H_2 Binding in Solid State Dihydrogen Complexes [M(η^2‑H_2)(CO)dppe_2][BArF^(24)] (M = Mn, Tc, Re): An Experimental and First Principles Study

    Abrecht, David G.; Fultz, Brent
    The solid state complex [Mn(CO)dppe_2][BArF^(24)] was synthesized, and the thermodynamic behavior and properties of the hydrogen absorption reaction to form the dihydrogen complex [Mn(η^2-H_2)dppe_2][BArF^(24)] were measured over the temperature range 313–373 K and pressure range 0–600 Torr using the Sieverts method. The absorption behavior was accurately described by Langmuir isotherms, and enthalpy and entropy values of ΔH° = −52.2 kJ/mol and ΔS° = −99.6 J/(mol K) for the absorption reaction were obtained from the Langmuir equilibrium constant. The observed binding strength was similar to metal hydrides and other organometallic complexes, despite rapid kinetics suggesting a site-binding mechanism similar to physisorption...

  11. Rapid self-assembly of brush block copolymers to photonic crystals

    Sveinbjörnsson, Benjamin R.; Weitekamp, Raymond A.; Miyake, Garret M.; Xia, Yan; Atwater, Harry A.; Grubbs, Robert H.
    The reduced chain entanglement of brush polymers over their linear analogs drastically lowers the energetic barriers to reorganization. In this report, we demonstrate the rapid self-assembly of brush block copolymers to nanostructures with photonic bandgaps spanning the entire visible spectrum, from ultraviolet (UV) to near infrared (NIR). Linear relationships were observed between the peak wavelengths of reflection and polymer molecular weights. This work enables “bottom-up” fabrication of photonic crystals with application-tailored bandgaps, through synthetic control of the polymer molecular weight and the method of self-assembly. These polymers could be developed into NIR-reflective paints, to combat the “urban heat island effect”...

  12. Synthesis of Isocyanate-Based Brush Block Copolymers and Their Rapid Self-Assembly to Infrared-Reflecting Photonic Crystals

    Miyake, Garret M.; Weitekamp, Raymond A.; Piunova, Victoria A.; Grubbs, Robert H.
    The synthesis of rigid-rod, helical isocyanate-based macromonomers was achieved through the polymerization of hexyl isocyanate and 4-phenylbutyl isocyanate, initiated by an exo-norbornene functionalized half-titanocene complex. Sequential ruthenium-mediated ring-opening metathesis polymerization of these macromonomers readily afforded well-defined brush block copolymers, with precisely tunable molecular weights ranging from high (1512 kDa) to ultrahigh (7119 kDa), while maintaining narrow molecular weight distributions (PDI = 1.08–1.39). The self-assembly of these brush block copolymers to solid thin-films and their photonic properties were investigated. Due to the rigid architecture of these novel polymeric materials, they rapidly self-assemble through simple controlled evaporation to photonic crystal materials that...

  13. Critical Materials For Sustainable Energy Applications

    Fromer, N. A.; Eggert, Roderick G.; Lifton, Jack

  14. In Situ Nanomechanical Measurements of Interfacial Strength in Membrane-Embedded Chemically Functionalized Si Microwires for Flexible Solar Cells

    Cho, Clara J.; O’Leary, Leslie; Lewis, Nathan S.; Greer, Julia R.
    Arrays of vertically aligned Si microwires embedded in polydimethylsiloxane (PDMS) have emerged as a promising candidate for use in solar energy conversion devices. Such structures are lightweight and concurrently demonstrate competitive efficiency and mechanical flexibility. To ensure reliable functioning under bending and flexing, strong interfacial adhesion between the nanowire and the matrix is needed. In situ uniaxial tensile tests of individual, chemically functionalized, Si microwires embedded in a compliant PDMS matrix reveal that chemical functionality on Si microwire surfaces is directly correlated with interfacial adhesion strength. Chemical functionalization can therefore serve as an effective methodology for accessing a wide range...

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