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Caltech Authors (143.226 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 7.213

  1. Robust causal transform coding for LQG systems with delay loss in communications

    Izadinasab, Mohammad Kazem; Sani, Amir Homayoun Bahari; Lahouti, Farshad; Hassibi, Babak
    A networked controlled system (NCS) in which the plant communicates to the controller over a channel with random delay loss is considered. The channel model is motivated by recent development of tree codes for NCS, which effectively translates an erasure channel to one with random delay. A causal transform coding scheme is presented which exploits the plant state memory for efficient communications (compression) and provides robustness to channel delay loss. In this setting, we analyze the performance of linear quadratic Gaussian (LQG) closed-loop systems and the design of the optimal controller. The design of the transform code for LQG systems...

  2. 3D velocity field time series using synthetic aperture radar: application to tidal-timescale ice-flow variability in Rutford Ice Stream, West Antarctica

    Milillo, Pietro; Minchew, Brent; Agram, Piyush; Riel, Bryan; Simons, Mark
    We present a general method for retrieving time-series of three component surface velocity field vector given a set of continuous synthetic aperture radar (SAR) acquisitions collected from multiple geometries. Our algorithm extends the single-line-of-sight mathematical framework developed for time-series analysis using interferometric SAR (InSAR) to three spatial dimensions. The inversion is driven by a design matrix corresponding to a dictionary of displacement functions parameterized in time. The resulting model minimizes a cost function using a non-regularized least-squares method. We applied our method to Rutford ice stream (RIS), West Antarctica, using a set of 101 multi-track multi-angle COSMO-SkyMed displacement maps generating...

  3. Minimally Invasive Parylene Dual-Valved Flow Drainage Shunt for Glaucoma Implant

    Lin, Jeffrey Chun-Hui; Chen, Po-Jui; Yu, Brian; Humayun, Mark; Tai, Yu-Chong
    A parylene-enabled microvalved shunt implant for glaucoma drainage is presented in this paper. Enabled by the dual-checkvalve operation, this device can physically drain the extra intraocular fluid and regulate the intraocular pressure (IOP) within the normal range (15-20 mmHg). Improved surgical features, in addition to the functional/microfluidic components, such as parylene-tube carrier and anchors, are also incorporated in such device to realize minimally invasive suture-less implantation, suitable for practical in vivo use. With the optimized micromachining and post-fabrication process procedures, the developed implant is the first checkvalved glaucoma drainage device (GDD), which is passive, consumes no additional power, and functions...

  4. Level Crossing in Toroidal on-Chip Microcavities

    Schwefel, Harald G. L.; Yang, Lan; Oxborrow, Mark; Stone, A. Douglas; Vahala, Kerry J.; Carmon, Tal
    Level crossing between optical whispering-gallery modes is studied in toroidal microcavities. We photograph azimuthal and radial envelope patterns of crossed optical modes. We also investigate anti-crossing between modes and polarization evolution.

  5. Scientific workflow applications on Amazon EC2

    Juve, Gideon; Deelman, Ewa; Vahi, Karan; Mehta, Gaurang; Berriman, Bruce; Berman, Benjamin P.; Maechling, Phil
    The proliferation of commercial cloud computing providers has generated significant interest in the scientific computing community. Much recent research has attempted to determine the benefits and drawbacks of cloud computing for scientific applications. Although clouds have many attractive features, such as virtualization, on-demand provisioning, and “pay as you go” usage-based pricing, it is not clear whether they are able to deliver the performance required for scientific applications at a reasonable price. In this paper we examine the performance and cost of clouds from the perspective of scientific workflow applications. We use three characteristic workflows to compare the performance of a...

  6. MySQL/PHP web database applications for IPAC proposal submission

    Crane, Megan K.; Storrie-Lombardi, Lisa J.; Silbermann, Nancy A.; Rebull, Luisa M.
    The Infrared Processing and Analysis Center (IPAC) is NASA's multi-mission center of expertise for long-wavelength astrophysics. Proposals for various IPAC missions and programs are ingested via MySQL/PHP web database applications. Proposers use web forms to enter coversheet information and upload PDF files related to the proposal. Upon proposal submission, a unique directory is created on the webserver into which all of the uploaded files are placed. The coversheet information is converted into a PDF file using a PHP extension called FPDF. The files are concatenated into one PDF file using the command-line tool pdftk and then forwarded to the review...

  7. SPRITE: the Spitzer proposal review website

    Crane, Megan K.; Storrie-Lombardi, Lisa J.; Silbermann, Nancy A.; Rebull, Luisa M.
    The Spitzer Science Center (SSC), located on the campus of the California Institute of Technology, supports the science operations of NASA's infrared Spitzer Space Telescope. The SSC issues an annual Call for Proposals inviting investigators worldwide to submit Spitzer Space Telescope proposals. The Spitzer Proposal Review Website (SPRITE) is a MySQL/PHP web database application designed to support the SSC proposal review process. Review panel members use the software to view, grade, and write comments about the proposals, and SSC support team members monitor the grading and ranking process and ultimately generate a ranked list of all the proposals. The software...

  8. Proposal review rankings: the influence of reviewer discussions on proposal selection

    Storrie-Lombardi, Lisa J.; Silbermann, Nancy A.; Rebull, Luisa M.; Laine, Seppo; Crane, Megan
    The telescope time allocation process for NASA's Great Observatories involves a substantial commitment of time and expertise by the astronomical community. The annual review meetings typically have 100 external participants. Each reviewer spends 3-6 days at the meeting in addition to one-two weeks of preparation time, reading and grading proposals. The reviewers grade the proposals based on their individual reading prior to the meeting and grade them again after discussion within the broad, subject-based review panels. We summarize here how the outcome of the review process for three Spitzer observing cycles would have changed if the selection had been done...

  9. Spitzer's model for dealing with the end of the cryogenic mission

    Dodd, Suzanne R.; Storrie-Lombardi, Lisa; Scott, Charles P.
    The Spitzer Space Telescope is a cryogenically cooled telescope operating three instruments in wavelengths ranging from 3.6 microns to 160 microns. Spitzer, the last of NASA's Great Observatories, was launched in August 2003 and has been operating for 4.5 years of an expected 5.5 year cryogen mission. The highly efficient Observatory has provided NASA and the science community with unprecedented data on galaxies, star formation, interstellar medium, exoplanets, and other fundamental astronomical topics. Spitzer's helium lifetime is predicted to end on April 18, 2009, with an uncertainty of +/- 3 months. Planning for this cryogen end involves many diverse areas...

  10. Hadoop distributed file system for the Grid

    Attebury, Garhan; Baranovski, Andrew; Bloom, Ken; Bockelman, Brian; Kcira, Dorian; Letts, James; Levshina, Tanya; Lundestedt, Carl; Martin, Terrence; Maier, Will; Pi, Haifeng; Rana, Abhishek; Sfiligoi, Igor; Sim, Alexander; Thomas, Michael; Wuerthwein, Frank
    Data distribution, storage and access are essential to CPU-intensive and data-intensive high performance Grid computing. A newly emerged file system, Hadoop distributed file system (HDFS), is deployed and tested within the Open Science Grid (OSG) middleware stack. Efforts have been taken to integrate HDFS with other Grid tools to build a complete service framework for the Storage Element (SE). Scalability tests show that sustained high inter-DataNode data transfer can be achieved for the cluster fully loaded with data-processing jobs. The WAN transfer to HDFS supported by BeStMan and tuned GridFTP servers shows large scalability and robustness of the system. The...

  11. On matrix factorization and finite-time average-consensus

    Ko, Chih-Kai; Gao, Xiaojie
    We study the finite-time average-consensus problem for arbitrary connected networks. Viewing this consensus problem as a factorization of 1/n11^T by suitable families of matrices, we prove the existence of a finite factorization and provide tight bounds on the size of the minimal factorization by exhibiting finite-time average-consensus algorithms and bounding their runtimes. We also show that basic matrix theory yields insights into the structure of finite-time consensus algorithms.

  12. Optimized DFT-FB transceivers over LTV channels

    Liu, Chih-Hao; Vaidyanathan, P. P.
    In this work, we consider the optimization of DFT modulated filterbank transceiver (DFT-FBT) over linear time varying (LTV) channels. The DFT-FBT is a generalization of the Affine Fourier transform based OFDM (Affine OFDM) and the chirped OFDM, which are suggested in recent literature for the transmission over LTV channels. For both known LTV channels and unknown wide sense stationary uncorrelated scattering (WSSUS) statistical channels, we show how to optimize the transmitting and receiving prototypes of DFT-FBT such that the signal to interference and noise ratio (SINR) at the receiver is maximized. After the optimization, the channel dependent part, like OFDM,...

  13. Generalized triangular transform coding

    Weng, Ching-Chih; Chen, Chun-Yang; Vaidyanathan, P. P.
    A general family of optimal transform coders (TC) is introduced here based on the generalized triangular decomposition (GTD) developed by Jiang, et al. This family includes the Karhunen-Loeve transform (KLT), and the prediction-based lower triangular transform (PLT) introduced by Phoong and Lin, as special cases. The coding gain of the entire family, with optimal bit allocation, is equal to those of the KLT and the PLT. Even though the PLT is not applicable for vectors which are not blocked versions of scalar wide sense stationary (WSS) processes, the GTD based family includes members which are natural extensions of the PLT,...

  14. Neighborhood gossip: Concurrent averaging through local interference

    Nazer, Bobak; Dimakis, Alexandros G.; Gastpar, Michael
    In this paper, we study a gossip algorithm for distributed averaging over a wireless sensor network. The usual assumption is that, through properly chosen codes, the physical layer is reduced to a set of reliable bit pipes for the distributed averaging algorithm. However, with a new channel coding technique, computation coding, we can exploit the interference property of the wireless medium for efficient averaging. This then provides a new abstraction for the physical layer: reliable linear equations instead of reliable bit pipes. The “neighborhood gossip” algorithm operates modularly on top of this abstraction. We will show that for certain regimes,...

  15. Planar Circularly Symmetric Electromagnetic Band-Gap antennas for low cost high performance integrated antennas

    Neto, A.; Llombart, N.; Gerini, G.; de Maagt, P. J.
    The use of Planar Circularly Symmetric (PCS) Electromagnetic Band-Gap (EBG) structures for optimizing the performances of single antenna elements and arrays is been discussed. The key advantage of using this sort of super structures is that they are planar and thus very cheap to manufacture with respect to alternative EBG structures based on vertical pins. In this contribution a review of the design principles and of the antennas based on PCS EBG which have been developed at TNO will be presented. Also a review of the applications that effectively used the benefit associated with them will be discussed. In conclusions,...

  16. Mid-IR-selected Quasars in the Spitzer First Look Survey

    Petric, A. O.; Lacy, M.; Storrie-Lombardi, L. J.; Sajina, A.; Armus, L.; Canalizo, G.; Ridgway, S.
    We present an investigation of the spectral energy distribution of mid-IR-selected quasars from the Spitzer First Look and SWIRE surveys. We explore a suite of clumpy torus models from Nenkova et al. (2002) to see how well they fit the types of objects we find. For about one-third of our objects these models underestimate the amount of observed 70 micron emission. We constrain the contribution and rough population age of the AGN hosts and use radio, 70 and 24 micron data to characterize the star-forming properties of these objects.

  17. Optical-IR SEDs of SDSS quasars in the Spitzer First Look Survey

    Richards, Gordon; Lacy, M.; Storrie-Lombardi, L.; Fan, X.; Papovich, C.; Gallagher, D.; Hall, P.; Hines, D.; Anderson, S.; Jester, S.; Schneider, D.; Vanden Berk, D.; Strauss, M.; York, D.
    We analyze the spectral energy distribution (SED) of SDSS-selected quasars in the Spitzer First Look Survey area. Optical+IR colors allow for efficient selection of quasars. We construct a mean quasar SED that can be used to learn about accretion disks, disk-winds, and dusty tori. Future improvements in determining multiwavelength SEDs of different classes of quasars are needed to improve estimates of physical parameters of quasars such as bolometric luminosities and accretion rates.

  18. Optimization of a metallo-dielectric EBG waveguide

    Mazzinghi, Agnese; Llombart, Nuria; Freni, Angelo; Siegel, Peter H.
    n this contribution we have presented a new metallo-dielectric EBG waveguide. The initial concept is based on Bragg fiber, which cross section is usually very large in terms of the wavelength. To reduce the waveguide dimensions and make it feasible at THz frequencies, we use a combination of a metallic and a dielectric waveguide. Standard resonant geometries will have high bend coupling between the TE01 and EH11 modes, thus reducing the losses introduced by the bend. Here we present two ways of optimizing the waveguide structure to break the degeneracy between these modes. One considers the periodicity along ρ and...

  19. Data movement in flash memories

    Jiang, Anxiao (Andrew); Langberg, Michael; Mateescu, Robert; Bruck, Jehoshua
    NAND flash memories are the most widely used non-volatile memories, and data movement is common in flash storage systems. We study data movement solutions that minimize the number of block erasures, which are very important for the efficiency and longevity of flash memories. To move data among n blocks with the help of Δ auxiliary blocks, where every block contains m pages, we present algorithms that use θ(n · min{m, log_Δ n}) erasures without the tool of coding. We prove this is almost the best possible for non-coding solutions by presenting a nearly matching lower bound. Optimal data movement can...

  20. Universal rewriting in constrained memories

    Jiang, Anxiao (Andrew); Langberg, Michael; Schwartz, Moshe; Bruck, Jehoshua
    A constrained memory is a storage device whose elements change their states under some constraints. A typical example is flash memories, in which cell levels are easy to increase but hard to decrease. In a general rewriting model, the stored data changes with some pattern determined by the application. In a constrained memory, an appropriate representation is needed for the stored data to enable efficient rewriting. In this paper, we define the general rewriting problem using a graph model. This model generalizes many known rewriting models such as floating codes, WOM codes, buffer codes, etc. We present a novel rewriting...

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