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Caltech Authors (129.911 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 5.969

  1. Virtual Observatory: From Concept to Implementation

    Djorgovski, S. G.; Williams, R.
    We review the origins of the Virtual Observatory (VO) concept, and the current status of the efforts in this field. VO is the response of the astronomical community to the challenges posed by the modern massive and complex data sets. It is a framework in which information technology is harnessed to organize, maintain, and explore the rich information content of the exponentially growing data sets, and to enable a qualitatively new science to be done with them. VO will become a complete, open, distributed, web-based framework for astronomy of the early 21st century. A number of significant efforts worldwide are...

  2. Convex Recovery of a Structured Signal from Independent Random Linear Measurements

    Tropp, Joel A.
    This chapter develops a theoretical analysis of the convex programming method for recovering a structured signal from independent random linear measurements. This technique delivers bounds for the sampling complexity that are similar to recent results for standard Gaussian measurements, but the argument applies to a much wider class of measurement ensembles. To demonstrate the power of this approach, the chapter presents a short analysis of phase retrieval by trace-norm minimization. The key technical tool is a framework, due to Mendelson and coauthors, for bounding a nonnegative empirical process.

  3. Transcriptional Regulation of T Cell Lineage Commitment

    Rothenberg, Ellen V.
    Through most of life, multilineage precursor cells undergo commitment to the T cell lineage only after immigrating to the thymus. These cells undergo a stepwise process through which they give up potential to become B cells, myeloid cells, dendritic cells, natural killer cells, or innate lymphoid cells. The commitment process involves separate mechanisms to deal with each of these options, with environmental Notch signaling deferring access to the alternative pathways through multiple rounds of cell division until permanent, intrinsic mechanisms of alternative fate exclusion can be established. The basis for measuring alternative lineage potential, the roles of environmental signals in...

  4. Oxygen-Evolving Complex of Photosystem II: Insights from Computation and Synthetic Models

    Kanady, Jacob S.; Mendoza-Cortés, José L.; Goddard, William A., III; Agapie, Theodor

  5. Multiple-Step Electron Flow in Proteins

    Warren, Jeffrey J.; Ener, Maraia E.; Winkler, Jay R.; Gray, Harry B.

  6. Live Staining of Drosophila Embryos with RPTP Fusion Proteins to Detect and Characterize Expression of Cell-Surface RPTP Ligands

    Bali, Namrata; Lee, Hyung-Kook (Peter); Zinn, Kai
    The activity and/or localization of receptor tyrosine kinases and phosphatases are controlled by binding to cell-surface or secreted ligands. Identification of ligands for receptor tyrosine phosphatases (RPTPs) is essential for understanding their in vivo functions during development and disease. Here we describe a novel in vivo method to identify ligands and binding partners for RPTPs by staining live-dissected Drosophila embryos. Live dissected embryos are incubated with RPTP fusion proteins to detect ligand binding in embryos. This method can be streamlined to perform large-scale screens for ligands as well as to search for embryonic phenotypes.

  7. Walking your dog in the woods in polynomial time

    Chambers, Erin Wolf; de Verdière, Éric Colin; Erickson, Jeff; Lazard, Sylvain; Lazarus, Francis; Thite, Shripad
    The Fréchet distance between two curves in the plane is the minimum length of a leash that allows a dog and its owner to walk along their respective curves, from one end to the other, without backtracking. We propose a natural extension of Fréchet distance to more general metric spaces, which requires the leash itself to move continuously over time. For example, for curves in the punctured plane, the leash cannot pass through or jump over the obstacles ("trees"). We describe a polynomial-time algorithm to compute the homotopic Fréchet distance between two given polygonal curves in the plane minus a...

  8. Using semantic content as cues for better scanpath prediction

    Cerf, Moran; Frady, E. Paxon; Koch, Christof
    Under natural viewing conditions, human observers use shifts in gaze to allocate processing resources to subsets of the visual input. There are many computational models that try to predict these shifts in eye movement and attention. Although the important role of high level stimulus properties (e.g., semantic information) stands undisputed, most models are based solely on low-level image properties. We here demonstrate that a combined model of high-level object detection and low-level saliency significantly outperforms a low-level saliency model in predicting locations humans fixate on. The data is based on eye-movement recordings of humans observing photographs of natural scenes, which contained one...

  9. The role of Bayesian bounds in comparing SLAM algorithms performance

    Censi, Andrea
    It is certainly hard to establish performance metrics for intelligent systems. Thankfully, no intelligence is needed to solve SLAM at all. Actually, when we cast the SLAM problem in the Bayesian framework, we already have a formula for the solution — SLAM research is essentially about finding good approximations to this computationally monstrous formula. Still, SLAM algorithms are difficult to analyze formally, partly because of such out-of-model ad hoc approximations. This paper explains the role of Bayesian bounds in the analysis of such algorithms, according to the principle that sometimes it is better to analyze the problem than the solutions. The...

  10. High-frequency simulations of global seismic wave propagation using SPECFEM3D_GLOBE on 62K processors

    Carrington, Laura; Komatitsch, Dimitri; Laurenzano, Michael; Tikir, Mustafa M.; Michéa, David; Snavely, Allan; Tromp, Jeroen
    SPECFEM3D_GLOBE is a spectral element application enabling the simulation of global seismic wave propagation in 3D anelastic, anisotropic, rotating and self-gravitating Earth models at unprecedented resolution. A fundamental challenge in global seismology is to model the propagation of waves with periods between 1 and 2 seconds, the highest frequency signals that can propagate clear across the Earth. These waves help reveal the 3D structure of the Earth's deep interior and can be compared to seismographic recordings. We broke the 2 second barrier using the 62K processor Ranger system at TACC. Indeed we broke the barrier using just half of Ranger,...

  11. High-density model for server allocation and placement

    Cameron, Craig W.; Low, Steven H.; Wei, David X.
    It is well known that optimal server placement is NP-hard. We present an approximate model for the case when both clients and servers are dense, and propose a simple server allocation and placement algorithm based on high-rate vector quantization theory. The key idea is to regard the location of a request as a random variable with probability density that is proportional to the demand at that location, and the problem of server placement as source coding, i.e., to optimally map a source value (request location) to a codeword (server location) to minimize distortion (network cost). This view has led to a...

  12. Cognitive hierarchy modelling of lab, field and neural data

    Camerer, Colin F.
    Cognitive hierarchy and level-k models assume players use steps of reasoning iteratively. Precision comes from making (and testing) various assumptions about the step distribution, beliefs of players at each step, and responsiveness to expected payoff. I describe several empirical examples of these models applied to lab experiments and two field settings. In addition, eyetracking and some neural evidence are supportive of the concept of limits of iterated thinking and suggest some interesting research directions.

  13. Molecular electronics: devices, systems and tools for gigagate, gigabit chips

    Butts, Michael; DeHon, André; Goldstein, Seth Copen
    New electronics technologies are emerging which may carry us beyond the limits of lithographic processing down to molecular-scale feature sizes. Devices and interconnects can be made from a variety of molecules and materials including bistable and switchable organic molecules, carbon nanotubes, and, single-crystal semiconductor nanowires. They can be self-assembled into organized structures and attached onto lithographic substrates. This tutorial reviews emerging molecular-scale electronics technology for CAD and system designers and highlights where ICCAD research can help support this technology.

  14. Active learning for directed exploration of complex systems

    Burl, Michael C.; Wang, Esther
    Physics-based simulation codes are widely used in science and engineering to model complex systems that would be infeasible to study otherwise. Such codes provide the highest-fidelity representation of system behavior, but are often so slow to run that insight into the system is limited. For example, conducting an exhaustive sweep over a d-dimensional input parameter space with ksteps along each dimension requires k^d simulation trials (translating into k^d CPU-days for one of our current simulations). An alternative is directed exploration in which the next simulation trials are cleverly chosen at each step. Given the results of previous trials, supervised learning techniques (SVM, KDE, GP) are applied to build up simplified predictive models of system behavior. These models...

  15. Computation and incentives in combinatorial public projects

    Buchfuhrer, Dave; Schapira, Michael; Singer, Yaron
    The Combinatorial Public Projects Problem (CPPP) is an abstraction of resource allocation problems in which agents have preferences over alternatives, and an outcome that is to be collectively shared by the agents is chosen so as to maximize the social welfare. We explore CPPP from both computational and mechanism design perspectives. We examine CPPP in the hierarchy of complement-free (subadditive) valuation classes and present positive and negative results for both unrestricted and truthful algorithms.

  16. Tensile Properties of Inkjet 3D Printed Parts: Critical Process Parameters and Their Efficient Analysis

    Mueller, Jochen; Kim, Shi En; Shea, Kristina; Daraio, Chiara
    To design and optimize for capabilities of additive manufacturing processes it is also necessary to understand and model their variations in geometric and mechanical properties. In this paper, such variations of inkjet 3D printed parts are systematically investigated by analyzing parameters of the whole process, i.e. storage of the material, printing, testing, and storage of finished parts. The goal is to both understand the process and determine the parameters that lead to the best mechanical properties and the most accurate geometric properties. Using models based on this understanding, we can design and optimize parts, and fabricate and test them successfully,...

  17. Performance Evaluation of FMOSSIM, a Concurrent Switch-Level Fault Simulator

    Bryant, Randal E.; Schuster, Michael D.
    This paper presents measurements obtained while performing fault simulations of MOS circuits modeled at the switch level. In this model the transistor structure of the circuit is represented explicitly as a network of charge storage nodes connected by bidirectional transistor switches. Since the logic model of the simulator closely matches the actual structure of MOS circuits, such faults as stuck-open and closed transistors as well as short and open-circuited wires can be simulated. By using concurrent simulation techniques, we obtain a performance level comparable to fault simulators using logic gate models. Our measurements indicate that fault simulation times grow as...

  18. An Initial Evaluation of the Tera Multithreaded Architecture and Programming System Using the C3I Parallel Benchmark Suite

    Burnett, Sharon; Thornley, John; Ellenbecker, Marrq
    The Tera Multithreaded Architecture (MTA) is a radical new architecture intended to revolutionize high-performance computing in both the scientific and commercial marketplaces. Each processor supports 128 threads in hardware. Extremely fast thread switching is used to mask latency in a uniform-access memory system without caching. It is claimed that these hardware characteristics allow compilers to easily transform sequential programs into efficient multithreaded programs for the Tera MTA. In this paper, we attempt to provide an objective initial evaluation of the performance of the Tera multithreaded architecture and programming system for general-purpose applications. The basis of our investigation is two programs...

  19. MAP: medial axis based geometric routing in sensor networks

    Bruck, Jehoshua; Gao, Jie; Jiang, Anxiao (Andrew)
    One of the challenging tasks in the deployment of dense wireless networks (like sensor networks) is in devising a routing scheme for node to node communication. Important consideration includes scalability, routing complexity, the length of the communication paths and the load sharing of the routes. In this paper, we show that a compact and expressive abstraction of network connectivity by the medial axis enables efficient and localized routing. We propose MAP, a Medial Axis based naming and routing Protocol that does not require locations, makes routing decisions locally, and achieves good load balancing. In its preprocessing phase, MAP constructs the medial...

  20. Localization and routing in sensor networks by local angle information

    Bruck, Jehoshua; Gao, Jie; Jiang, Anxiao (Andrew)
    Location information is very useful in the design of sensor network infrastructures. In this paper, we study the anchor-free 2D localization problem by using local angle measurements in a sensor network. We prove that given a unit disk graph and the angles between adjacent edges, it is NP-hard to find a valid embedding in the plane such that neighboring nodes are within distance 1 from each other and non-neighboring nodes are at least distance 1 away. Despite the negative results, however, one can find a planar spanner of a unit disk graph by using only local angles. The planar spanner can...

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