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Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

Type = Conference or Workshop Item

Mostrando recursos 1 - 20 de 762

  1. Learning-Based Abstractions for Nonlinear Constraint Solving

    Dathathri, Sumanth; Aréchiga, Nikos; Gao, Sicun; Murray, Richard M.
    We propose a new abstraction refinement procedure based on machine learning to improve the performance of nonlinear constraint solving algorithms on large-scale problems. The proposed approach decomposes the original set of constraints into smaller subsets, and uses learning algorithms to propose sequences of abstractions that take the form of conjunctions of classifiers. The core procedure is a refinement loop that keeps improving the learned results based on counterexamples that are obtained from partial constraints that are easy to solve. Experiments show that the proposed techniques significantly improved the performance of state-of-the-art constraint solvers on many challenging benchmarks. The mechanism is...

  2. Reducing Versatile Bat Wing Conformations to a 1-DoF Machine

    Hoff, Jonathan; Ramezani, Alireza; Chung, Soon-Jo; Hutchinson, Seth
    Recent works have shown success in mimicking the flapping flight of bats on the robotic platform Bat Bot (B2). This robot has only five actuators but retains the ability to flap and fold-unfold its wings in flight. However, this bat-like robot has been unable to perform folding-unfolding of its wings within the period of a wingbeat cycle, about 100 ms. The DC motors operating the spindle mechanisms cannot attain this folding speed. Biological bats rely on this periodic folding of their wings during the upstroke of the wingbeat cycle. It reduces the moment of inertia of the wings and limits...

  3. From Rousettus aegyptiacus (bat) Landing to Robotic Landing: Regulation of CG-CP Distance Using a Nonlinear Closed-Loop Feedback

    Syed, Usman A.; Ramezani, Alireza; Chung, Soon-Jo; Hutchinson, Seth
    Bats are unique in that they can achieve unrivaled agile maneuvers due to their functionally versatile wing conformations. Among these maneuvers, roosting (landing) has captured attentions because bats perform this acrobatic maneuver with a great composure. This work attempts to reconstruct bat landing maneuvers with a Micro Aerial Vehicle (MAV) called Allice. Allice is capable of adjusting the position of its Center of Gravity (CG) with respect to the Center of Pressure (CP) using a nonlinear closed-loop feedback. This nonlinear control law, which is based on the method of input-output feedback linearization, enables attitude regulations through variations in CG-CP distance....

  4. Describing Robotic Bat Flight with Stable Periodic Orbits

    Ramezani, Alireza; Ahmed, Syed Usman; Hoff, Jonathan; Chung, Soon-Jo; Hutchinson, Seth
    From a dynamic system point of view, bat locomotion stands out among other forms of flight. During a large part of bat wingbeat cycle the moving body is not in a static equilibrium. This is in sharp contrast to what we observe in other simpler forms of flight such as insects, which stay at their static equilibrium. Encouraged by biological examinations that have revealed bats exhibit periodic and stable limit cycles, this work demonstrates that one effective approach to stabilize articulated flying robots with bat morphology is locating feasible limit cycles for these robots; then, designing controllers that retain the closed-loop...

  5. Cell-selective proteomic analysis of host-microbe interactions using Bio-orthogonal Noncanonical Amino Acid Tagging (BONCAT)

    Stone, Shannon; Shon, Judy; Khosravi, Arya; Sweredoski, Michael; Moradian, Annie; Hess, Sonja; Mazmanian, Sarkis; Tirrell, David A.
    While proteomic studies of microbes in culture have provided many important biol. insights, there is a need for more global analyses of their behavior during interactions within mammalian hosts. However, abundant host tissues often dominate and obstruct system-wide profiling of proteins expressed by microbes in mouse models. We have adapted bio-orthogonal non-canonical amino add tagging (BONCAT), a chemoproteomic tool for detecting newly-synthesized proteins in complex biol. systems, to cell-selectively label and identify microbial proteins while infecting or colonizing a live mouse. Diverse species of microbes have been labeled using this technique, Including methicillin-resistant Staphylococcus aureus (MRSA), and the human gut commensal,...

  6. Reaction mechanisms for the electrochemical reduction of CO_2 on the Cu(100) surface from quantum mechanics free energy calculations with explicit water

    Cheng, Tao; Xiao, Hai; Goddard, William A.
    Copper (Cu) is the only elemental metal that electrochem. catalyzes formation of significant amts. of hydrocarbons, but it requires a high overpotential (0.9 V) for a reasonable current, and it leads to a mix of major products [including hydrogen (H_2), ethylene (C_2H_4), and methane (CH_4)] plus small amts. of other C 's, C 's and oxygenates. Due to its unique ability to catalyze hydrocarbon formation, Cu is a prototype to det. and validate the mechanism of hydrocarbon formation, to serve as the basis for designing new catalysts that increase product selectivity and rates while simultaneously lowering overpotentials. Here, we carry out...

  7. Finite Temperature Density Matrix Embedding Theory

    Sun, Chong; Chan, Garnet
    Density Matrix Embedding Theory (DMET) provides a powerful and less expensive framework to treat strongly correlated ground-state problems in both solids and molecules, by reproducing the entanglement between the fragment and its environment at mean-field level, while the fragment is treated at a more accurate level. In this talk, I will extend the ground-state DMET to finite temperature DMET (FT-DMET), by solving both the mean-field problem and impurity problem at finite temperature T, and reconstructing bath orbitals from the mean-field solution. The finite temperature Lanczos algorithm as an alternative of full configuration interaction (FCI) is used to implement the impurity...

  8. Density Matrix Embedding Theory for Symmetry Protected Topological Systems

    Ray, Ushnish; Chan, Garnet
    Density Matrix Embedding Theory (DMET) presents a novel approach in capturing the physics of strongly correlated systems. It essentially describes finite fragments in the presence of environment while explicitly allowing quantum entanglement between both. DMET has been remarkably successful in studying systems ranging from molecules to solids and the paradigmatic Hubbard model. In this talk, we will present extensions of DMET to systems that are allowed to break SU(2) spin symmetry as well as U(1) particle number symmetry. This will enable us to study a range of broken symmetry phases such as topological superconductivity and, more interestingly, their interplay with...

  9. Development of a high-throughput immunofluorescence assay platform using a DNA-encoded streptavidin library for the rapid evaluation of protein-catalyzed capture agents

    McCarthy, Amy; Kim, Jungwoo; Henning, Ryan; Mishra, Anvita; Ng, Rachel; Museth, Anna; Heath, John; Winson, Emma; Oh, JunHyuck; Heath, James R.
    Protein Catalyzed Capture (PCC) Agents are an emergent class of macrocyclic peptides that selectively bind, with low NM affinities, to unique epitopes of specific proteins, such as oncoproteins and blood protein biomarkers. The development of a PCC binder is a robust process that involves screening a two million elements one-bead-one-compd. (OBOC) macrocyclic peptide library against a synthetic polypeptide representing the epitope of interest. A single generation screen is sufficient to identify candidate PCC ligands. Each candidate is tested via a series of binding assays to identify a PCC with optimal avidity characteristics. Such testing requires running multiple binding curve assays in...

  10. High throughput discovery of solar fuels photoanodes

    Gregoire, John
    The High Throughput Experimentation (HTE) project of the Joint Center for Artificial Photosynthesis performs accelerated discovery of earth-abundant photoelectrocatalysts and other solar fuels materials. The HTE materials discovery framework integrates experimentation with materials theory and has recently been deployed for the identification of several new classes of metal oxide photoelectrocatalysts for the oxygen evolution reaction. Through compilation and inspection of these discoveries, relationships among compn., structure, electronic structure, stability, photoactivity, band gap energy, etc. are being identified, providing a deeper understanding of the known materials and enabling the design of new photoanode materials. In addn. to introducing the materials discovery pipeline,...

  11. Plasmon-Driven photoelectrochemical cells for artiftcial photosynthesis

    Du Chene, Joseph; Tagliabue, Giulia; Welch, Alex J.; Yang, Qin; Reidy, Kate; Davoyan, Artur R.; Hsiow, Chuen-Yo; Atwater, Harry
    Artificial photosynthesis requires a material system that can harvest sunlight, carbon dioxide (CO_2), and water to produce chem. products (e.g. ethanol) in a solar-to-fuel process analogous to that employed by photosynthetic plants. Despite much promise, current CO_2-redn. catalysts require significant electrochem. overpotentials to achieve adequate activity while lacking appreciable chem. selectivity for a given product of interest. Numerous chem. compels. are often co-evolved during electrocatalytlc operation that are difficult to effectively sep. It is further noted that most catalysts operate under dark conditions through an applied elec. bias, but these reactions must ultimately be driven by excited-state carriers produced via...

  12. Tissue-specific ascaroside production in the nematode Caenorhabditis elegans

    Akagi, Allison E.; Sternberg, Paul; Schroeder, Frank
    Ascarosides are a family of small mols. used as signals in a variety of important behaviors in C. elegans and other nematodes; these include mate attraction, aggression, repulsion, and entry into dauer diapause under stressful conditions. Structurally, ascarosides are modular glycosides of the dideoxysugar ascarylose. Small structural changes in the fatty add moiety attached to the first position of the sugar as well as the addn. of other metabolically-derived components to the fourth position have been shown to elicit different behaviors. DAF-22, a thiolase responsible for the last step of peroxisomal beta-oxidn. of the ascaroside lipid side chain, is necessary...

  13. Noncovalent modulation of protein energy landscapes with an emerging class of cyclic-peptide chaperones

    Bunck, David N.; Atsavaprannee, Beatriz; Museth, Katrine; Heath, James R.
    Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease caused by the deterioration of motor neurons that abates essential biol. functions and exhibits survival times of 3 - 5 years after diagnosis. One driver of this disease derives from inherited mutations to the protein superoxide dismutase 1 (SOD1), which hinder proper folding and result in the accumulation of toxic aggregates. We identified cyclic peptides that target precise epitopes on SOD1 through a new high-throughput screening platform that furnishes high-affinity binders against regions of a protein independent of secondary and tertiary structure. Binding these epitopes both stabilizes the native state and accelerates folding....

  14. Solar fuels photoanodes prepared by inkjet printing of copper vanadates

    Newhouse, Paul; Boyd, David; Shinde, Aniketa; Guevarra, Dan; Zhou, Lan; Soedarmadji, Edwin; Li, Guo; Neaton, Jeffrey B.; Gregoire, John M.
    Widespread deployment of solar fuel generators requires the development of efficient and scalable functional materials, esp. for photoelectrocatalysis of the oxygen evolution reaction. Metal oxides comprise the most promising class of photoanode materials, but no known material meets the demanding photoelectrochem. requirements. Copper vanadates have recently been identified as a promising class of photoanode materials with several phases exhibiting an indirect band gap near 2 eV and stable photoelectrocatalysis of the oxygen evolution reaction in a pH 9.2 electrolyte. By employing combinatorial inkjet printing of metal precursors and applying both caldnation and rapid thermal processing, we characterize the phase behavior of...

  15. Sunlight-driven hydrogen formation by membrane-supported photoelectrochemical water splitting

    Lewis, Nathan S.
    We are developing an artificial photosynthetic system that utilizes sunlight and water as the inputs and produce hydrogen and oxygen as the outputs. We are taking a modular, parallel development approach in which three distinct primary components-the photoanode, the photocathode, and the product-sepg. but ion-conducting membrane-are fabricated and optimized sep. before assembly into a complete water-splitting system. The design principles incorporate two sep., photosensitive semiconductor/liq. junctions that will collectively generate the 1.7-1.9 Vat open circuit necessary to support both the oxldn. of H_2O (or OH‾) and the redn. of H+ (or H_2O). The photoanode and photocathode will consist of rod-like...

  16. Resonantly excited photocatalysts and light absorbers for solar fuels

    Atwater, Harry
    Excited electronic states in semiconductors and metals have the potential to alter the rate and selectivity of mol. redn. and oxidn. reactions in photocatalysis. Doing so requires an accurate description and understanding of resonant optical absorption, excited carrier generation, relaxation and interfacial charge transfer processes, so as to understand the prospects for directing catalytic processes with optically generated excited carriers. Advances in theory and simulation of excited state carrier generation and transport processes will be discussed, as well as new exptl. developments in optical design of resonant photocatalysts and photoelectrodes fuel solar fuel generators.

  17. Development of solar fuels photoanodes through combinatorial integration of Ni- La-Co-Ce oxide and Ni-Fe-Co-Ce oxide catalysts on BiVO4

    Haber, Joel; Guevarra, Dan; Shinde, Aniketa; Zhou, Lan; Li, Guo; Liu, Guiji; Sharp, Ian; Neaton, Jeffrey B.; Toma, Francesca M.; Gregoire, John
    The development of an efficient, stable photoanode provide protons and electrons to the (photo)cathode remains a primary materials challenge in the establishment of a scalable technol. for solar fuels generation. The typical photoanode architecture consists of a semiconductor light absorber coated with a metal oxide that serves a combination of functions, including corrosion protection, electrocatalysis, light trapping, hole transport, and elimination of deleterious recombination sites. To provide a more efficient exploration of metal oxide coatings for a given light absorber, we introduce a high throughput methodol. wherein a uniform BIVO_4 library is coated with 858 unique metal oxides covering a...

  18. Exploring the mechanism of action of a newly-discovered therapeutic peptide for blinding retinal diseases by identifying its receptors

    Zhou, Dan; Shao, Zixuan; Kornfield, Julia A.
    Diabetic and age-related retinopathies, both assocd. with growth of abnormal blood vessels, are leading causes of blindness in the developed world. Current treatments, such as Laser Photocoagulation and anti-Vascular Endothelial Growth Factor (VEGF) drugs, have limited efficacy and undesirable side effects. A recently discovered therapeutic peptide Luminate has proven to be effective in human clin. trials. Over half of the patients in phase I human clin. trial demonstrated vision improvement with 4 lines or over, and in some patients, the macular thicknesses was reduced back to the healthy state. It has shown significantly longer lasting benefits than anti-VEGF treatments and shows...

  19. Juice from juice: Bringing solar energy education to the classroom

    DeBoever, Michelle; Schuttlefield Christus, Jennifer D.
    The Center for Chem. Innovation in Solar Fuels (CCI Solar) has developed several diverse outreach programs over the 10 years of its existence that satisfy the National Science Foundation's Broader Impacts requirements, including citizen science, informal science education, and teacher professional development. Started in 2008, Juice from Juice is a teacher professional development program where researchers from the Center put on workshops for local teachers to introduce them to solar energy expts. and curriculum that they can implement in their classrooms. The program was originally local to the Pasadena area centered on the CCI's headquarters at Caltech. Teachers from the...

  20. Tweet, for science!: A social media course for scientists at Caltech tackling inreach and outreach online

    Wilkins, Olivia; Davis, Mark E.; Mojarad, Sarah
    The public places greater trust in scientists than in conventional media outlets for communicating science, and yet STEM topics are among the least represented areas on social media platforms. As technol. evolves, so do tools for online communication. Hence it is imperative that scientists develop and implement skills to use social media effectively. In Social Media for Scientists at the California Institute of Technol., students are introduced to how social media and science intersect and learn how to use social media for both inreach (engaging each other) and outreach (engaging general audiences). In the course, co-taught by a Chem. Engineering professor (Mark...

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