Recursos de colección
Caltech Authors (136.887 recursos)
Repository of works by Caltech published authors.
Type = Conference or Workshop Item
Repository of works by Caltech published authors.
Type = Conference or Workshop Item
Dathathri, Sumanth; Arechiga, Nikos; Gao, Sicun
This work addresses the problem of scalable constraint solving. Our technique combines traditional constraint-solving approaches with machine learning techniques to propose abstractions that simplify the problem. First, we use a collection of heuristics to learn sets of constraints that may be well abstracted as a single, simpler constraint. Next, we use an asymmetric machine learning procedure to abstract the set of clauses, using satisfying and falsifying instances as training data. Next, we solve a reduced constraint problem to check that the learned formula is indeed a consequent (or antecedent) of the formula we sought to abstract, and finally we use the learned formula to check the original property. Our experiments...
Blanco, Mario; Pickar, Kenneth; Delgado, Luz Marina; Kranski, Jeff; Arce, Oscar; Herrera, Francoise; MacVean, Charles
The World Bank estimates that over 2.8 billion people live in poverty, earning less than $2/day. Financial assistance alone has not been able to solve the problems generated by poverty in a sustainable way. We are testing the hypothesis that the teaching of product design principles together with basic entrepreneurship skills might be a way to provide longer-lasting solutions. These ideas are based on the premise that although cash might be the most pressing need of the poor, the most vital need is the acquisition of income generation skills. Major challenges arose in the initial testing stage, from the formidable physical and cultural...
Franck, Jennifer; Yu, Ted; Ochoa-Ricoux, Juan Pedro; Maloney, James; Capece, Angela; Rivas, Luz
The Young Engineering and Science Scholars (YESS) three-week summer program offered by the California Institute of Technology (Caltech) recruits and inspires talented high school students towards engineering and science career paths. The program is geared towards highachieving, but traditionally underrepresented minority students in science and engineering who have demonstrated excellent academic records in math and science. This paper describes the science and engineering course offered by the program including its objectives, teaching philosophies, and its mentoring process for design and research projects. Assessment is performed using the Force Concept Inventory (FCI) and shows excellent student gains when compared with other college-level physics courses. Student surveys and feedback on...
Jackson, Winston; Franck, Jennifer; Maloney, James; Ochoa-Ricoux, Juan Pedro; Rimoli, Julian; Rivas, Luz
Many outreach programs offered by universities provide pre-college students an opportunity to explore careers in science and engineering. For high-achieving students who already have an interest in these areas, these types of programs can introduce students to advanced concepts, develop their understanding of scientific methodologies, and expose them to science and engineering research. One such program, the Young Engineering and Science Scholars (YESS) Program, is a three-week summer residential program created to bring exceptional high school juniors and seniors from underrepresented minority groups to study at the California Institute of Technology (Caltech). The program is intended for motivated students who wish to broaden their knowledge of science and...
Gomez, Tara; Loson, Oliver; Yung, Douglas; Kadambi, Sindhuja; Lee, Paul; Rivas, Luz
The YESS program is a three-week summer residential course that brings together extraordinarily talented high school students from underrepresented minority groups to study at the California Institute of Technology. The YESS program is intended for students who exhibit an interest in engineering and science, and wish to engage in collaborative learning. During the three-week program, students take science courses and are exposed to laboratory tours, faculty lectures, and college admissions workshops. The neuroscience course for the 2008 YESS program was an intensive survey of many different fields, and used lectures, demonstrations and laboratory activities to teach topics such as brain anatomy, Drosophila melanogaster pain perception, electrophysiology,...
Maloney, James; Gomez, Tara; Franck, Jennifer; Aschbacher, Pamela
Liu, Chun-Lin; Vaidyanathan, P. P.
Two-dimensional sparse arrays with hole-free difference coarrays, like billboard arrays and open box arrays, can identify O(N^2) uncorrelated source directions (DOA) using N sensors. These arrays contain some dense ULA segments, leading to many sensor pairs separated by λ/2. The DOA estimation performance often suffers degradation due to mutual coupling between such closely-spaced sensor pairs. This paper introduces a new 2D array called the half open box array. For a given N, this array has the same hole-free coarray as an open box array. At the same time, the number of sensor pairs with small separation is significantly reduced.
Gray, Harry B.
The dianionic oxo ligand occupies a very special place in coordination chem., owing to its ability to donate pi electrons to stabilize high oxidn. states of metals. My papers on the ligand field theory of multiple bonding in metal-oxos were published over 50 years ago in the first vol. of Inorg. Chem. The theory, which accounts for the optical and EPR spectroscopic properties of these complexes, also predicts that there must be an "oxo wall" between Fe-Ru-Os and Co-Rh-Ir in the periodic table. There have been many attempts to break down the wall, but it is still in pretty good...
Politzer, H. David
Kim, Joey; Hadjichristidis, Nikos; Kornfield, Julia
The natural building blocks of linear polymer are monomers. Similarly, the natural building blocks of bottblebrush polymers are linear polymers (commonly referred to as polymacromonomers). It is well established that many properties of linear polymers can be tuned by using different copolymer systems. Similarly, we expect tunability of bottlebrush polymers by using chem. distinct polymer chains. A collaborative effort with Hadjichristidis from KAUST led us to a deeper study on the arrangement of chem. distinct polymeric units within the bottlebrush architecture. We have organized these samples into four categories based on the geometric connectivity: homo-bottlebrush polymer (H) in which all side chains have identical chem. functionality,...
The first report of a noble gas compd., by Neil Bartlett in 1962, was quickly followed by a no. of others. Of course there ha been previous attempts, of which the best documented is probably that of Caltech inorg. chem. professor Donald Yost and student Albert Kaye; details of their unsuccessful expts. aimed at getting xenon to react with fluorine or chlorine were publ in JACS in 1933. After Bartlett"s success, a no. of commentators looked back to Yost"s paper and offered a variety of poss reasons for Yost"s failure. Examn. of the actual details of Yost's paper, in comparison with those of the...
Complex inorg. cofactors perform challenging catalytic transformations in biol. systems, such as photosystem II and nitrogenase. The effect of cluster structure on the phys. and chem. properties of these active sites is not well understood. We have developed methodologies for the rational synthesis of tetranuclear homo- and hetero-metallic clusters. The effect of metal compn. on redn. potentials has been correlated to Lewis acidity for redox inactive metals. Clusters with open coordination site have been prepd. for small mol. activation. CH and CF oxygenation has been obsd. for putative terminal Fe-oxo species supported by tetranuclear clusters. Tetranuclear clusters with bridging fluoride and oxide interstitial ligands have been...
Cannon, Jeff; Luo, Shaoxiong; Engle, Keary; Taylor, Buck; Houk, Kendall; Grubbs, Robert
A method for olefin metathesis between 3(E)-1,3-dienes and terminal olefins is described. The method employs a recently reported ruthenium-based catalyst contg. a cyclometalated NHC ligand and takes advantage of its pronounced selectivity for terminal olefins in the presence of internal E-olefins. A wide variety of functional groups can be tolerated. Applications of the reaction include direct synthesis of insect pheromones from commerical precursor.
The chem. synthesis of natural products provides an exciting platform from which to conduct fundamental research in chem. and biol. We are currently focused on devising concise approaches to complex polycyclic natural products such as ryanodol, acutumine, and members of the diterpenoid alkaloids. The densely packed arrays of heteroatoms and stereogenic centers that constitute these polycyclic targets challenge the limits of current technol. and inspire the development of new synthetic strategies and tactics. This seminar will describe our latest progress in both our methodol. and target-directed synthesis endeavors.
The common small objects in the Kuiper belt come in two colors: red and very red. Such a strong bifurcation in what must be chemical properties is extremely hard to explain through standard ideas of outer solar system mixing, accretion and formation. We have proposed that, instead, all objects start with essentially identical chemical composition, but, after formation has ended and the nebula has dispersed, icy outer solar system objects all go through a cometary phase where surface volatiles are removed. Volatile removal is an exponential function of surface temperature, thus volatile evaporation lines will be imposed across the outer...
Nickel-catalyzed reductive cross-coupling reactions have emerged as direct bond formation. These reactions typically tolerate an array of functional groups, and employ inexpensive, earth abundant metals as stoichiometric reductants. May require the use of pre-generated organometallic reagents. In order to realize the catalyzed reductive cross-coupling reactions, it is crit. to develop enantioselective transformations. This seminar will describe our recent successes in the develop enantioselective cross-coupling reactions.
Many important biological processes – ranging from simple metabolism to complex cognition – take place deep inside living organisms, yet our ability to study them in this context is limited. Technologies such as fluorescent and luminescent proteins enable exquisitely precise imaging of genetically specific cellular function in small and translucent specimens, but are limited by the poor penetration of light into larger tissues. In contrast, most non-invasive technologies such as magnetic resonance imaging (MRI) and ultrasound – while based on energy forms that penetrate tissue effectively – lack the needed molecular precision. Our work attempts to bridge this gap by...
Edwards, Julian; Zhang, Hefeng; Hadjichristidis, Nikos; Pasch, Harald; Vlassopoulos, Dimitris; Grubbs, Robert
The means to produce cyclic polymers in high purity and at large scale remains an elusive goal. Although ring-closure methods have been successful in producing rings free of linear chains, scalability is an unavoidable obstacle. We report a ring-expansion method for synthesizing cyclic polyalkenamers in high purity and at scale ( > 25 g / reaction) using a recyclable heterogeneous ruthenium-based olefin metathesis catalyst. This ring-expansion metathesis polymn. (REMP) catalyst is an analog of the 2nd Generation Hoveyda-Grubbs catalyst and is covalently bound to a silica surface via dual tethers from the N-heterocyclic carbene (NHC) and benzylidene. Cyclic polyalkenamers were synthesized from a variety of cycloolefins,...
Atm. aerosols interact directly and indirectly with the Earth"s radiation budget a effect, aerosols scatter and absorb solar radiation. Also, aerosols indirectly impac development, lifetime, pptn., and albedo. Current understanding of the aerosol uncertain, constituting the greatest uncertainty in climate predictions. In this pr to quantify the climate impacts of aerosol-cloud-radiation interactions using will be reviewed.
Radlauer, Madalyn; Agapie, Theodor; Hillmyer, Marc
Proximity and sterics play a large role in polymn. and polymer chem. In the bimetallic polymn. catalysts where the two metal centers are held on the sam ligand framework, the proximity of the second metal changes reactivity a enhancements of polar group tolerance or isoselecitivity in olefin polymn. are no systems with distal metal centers or in monometallic analogs. In cross metathes chains, high E-stereoregularity and head-to-tail regioregularity are achieved w generation catalysts when there is allylic substitution directing reactivity through polymers, the proximity of incompatible blocks due to a covalent connection system. This frustration can produce interesting and complicated morphologies where thermodn. penalties are expected to minimize the...