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Caltech Authors (132.208 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 6.072

  1. Robust Ambulance Allocation Using Risk-based Metrics

    Krishnan, Kaushik; Marla, Lavanya; Yue, Yisong
    This paper focuses on robust location strategies for a fleet of ambulances in cities in order to maximize service levels under unexpected demand patterns. Our work is motivated by the fact that when small parts of networks incur emergencies according to a heavy-tailed distribution, the structure of the network under resource constraints results in the entire system behaving in a heavy-tailed manner. To address this, metrics other than average-case need to be used. We achieve robust location strategies by including risk metrics that account for tail behavior and not average performance alone. Because of the exponentially large solution space for...

  2. VIP: Joint Traffic Engineering and Caching in Named Data Networks

    Yeh, Edmund; Ho, Tracey; Cui, Ying; Burd, Michael; Liu, Ran; Leong, Derek
    Emerging information-centric networking architectures seek to optimally utilize both bandwidth and storage for efficient content distribution. This highlights the need for joint design of traffic engineering and caching strategies. We present a systematic framework for joint dynamic interest request forwarding and dynamic cache placement and eviction, within the context of the Named Data Networking (NDN) architecture. The framework employs a virtual control plane which operates on the user demand rate for data objects in the network, and an actual plane which handles Interest Packets and Data Packets. We develop distributed algorithms within the virtual plane to achieve network load balancing...

  3. A study of polar codes for MLC NAND flash memories

    Li, Yue; Alhussien, Hakim; Haratsch, Erich F.; Jiang, Anxiao (Andrew)
    The increasing density of NAND flash memories makes data more prone to errors due to severe process variations and disturbance. The urgency to improve NAND flash reliability encourages searching for optimal channel coding methods. This paper reports our efforts towards a read channel for flash memories using polar coding. Our contributions include the solutions to several challenges raised when applying polar codes to NAND flash memories in practice. We propose efficient schemes for shortening both non-systematic and systematic polar codes, making polar codewords be easily adapted to flash page of any size. We demonstrate that the decoding performance of the...

  4. Optimizing Energy Storage Participation in Emerging Power Markets

    Chen, Hao; Liu, Zhenhuan; Coskun, Ayse K.; Wierman, Adam
    The growing amount of intermittent renewables in power generation creates challenges for real-time matching of supply and demand in the power grid. Emerging ancillary power markets provide new incentives to consumers (e.g., electrical vehicles, data centers, and others) to perform demand response to help stabilize the electricity grid. A promising class of potential demand response providers includes energy storage systems (ESSs). This paper evaluates the benefits of using various types of novel ESS technologies for a variety of emerging smart grid demand response programs, such as regulation services reserves (RSRs), contingency reserves, and peak shaving. We model, formulate and solve...

  5. A Comparison of the Determination of Closure Phase in Optical Interferometry with Fully Filled Apertures and Non-Redundant Aperture Masks

    Readhead, A. C. S.

  6. High Order Super Nested Arrays

    Liu, Chun-Lin; Vaidyanathan, P. P.
    Mutual coupling between sensors has a negative impact on the estimation of directions of arrival (DOAs). Sparse arrays such as nested arrays, coprime arrays, and minimum redundancy arrays (MRAs) have less mutual coupling than uniform linear arrays (ULAs). These sparse arrays also have a difference coarray of size O(N^2), where N is the number of sensors, and can therefore resolve O(N^2) uncorrelated source directions. The various sparse arrays proposed in the literature have their pros and cons. The nested array is practical and easy to use but has a dense ULA part which suffers from mutual coupling effects like the...

  7. Application of the Evolution-Variable Manifold Approach to Cavity-Stabilized Ethylene Combustion

    Cymbalist, Niccolo; Candler, Graham V.; Dimotakis, Paul E.
    For combustion in high-speed flows, radical-formation time scales and ignition delay times may be similar to, or dominate, relevant flow time scales. Reliable modeling of induction and autoignition processes is critical to the prediction of combustor performance. The evolution-variable manifold (EVM) approach of Cymbalist and Dimotakis uses a transported scalar to track the evolution of the reaction processes, from induction leading to autoignition and subsequent robust combustion. In the present work, the EVM method is implemented in a computational fluid dynamics code in which wall-modeled large-eddy simulations are performed for two ethylene-air high-speed combustion cases. The detailed thermochemical state of the...

  8. Cataloging Public Objects Using Aerial and Street-Level Images – Urban Trees

    Wegner, Jan D.; Branson, Steve; Hall, David; Schindler, Konrad; Perona, Pietro
    Each corner of the inhabited world is imaged from multiple viewpoints with increasing frequency. Online map services like Google Maps or Here Maps provide direct access to huge amounts of densely sampled, georeferenced images from street view and aerial perspective. There is an opportunity to design computer vision systems that will help us search, catalog and monitor public infrastructure, buildings and artifacts. We explore the architecture and feasibility of such a system. The main technical challenge is combining test time information from multiple views of each geographic location (e.g., aerial and street views). We implement two modules: det2geo, which detects...

  9. Chip-scale optical resonator enabled synthesizer (CORES) miniature systems for optical frequency synthesis

    Bowers, J. E.; Beling, A.; Blumenthal, D.; Bluestone, A.; Bowers, S. M.; Briles, T. C.; Chang, L.; Diddams, S. A.; Fish, G.; Guo, H.; Kippenberg, T. J.; Komljenovic, T.; Norberg, E.; Papp, S.; Pfeiffer, M. H. P.; Srinivasan, K.; Theogarajan, L.; Vahala, K. J.; Volet, N.
    An approach for a low-power chip-scale package is described, that provides a laser output with a programmable frequency across 50 nm of bandwidth centered at 1550 nm, and a resolution of one part in 10^(14).

  10. New directions for optical frequency division: Soliton microcombs and electro-optical-modulation

    Vahala, Kerry
    Optical frequency division based on mode-locked laser frequency combs makes possible the coherent transfer of frequency stability from optical systems to electronics. It has enabled a revolution in time keeping and frequency metrology. In this paper we describe progress on new methods for frequency comb generation including whispering-gallery-based microcombs and electro-optical comb generation. Demonstration of optical frequency division to produce stable microwaves using these new approaches will be discussed.

  11. Holographic microscopy for 3D tracking of bacteria

    Nadeau, Jay; Cho, Yong Bin; El-Kholy, Marwan; Bedrossian, Manuel; Rider, Stephanie; Lindensmith, Christian; Wallace, J. Kent
    Understanding when, how, and if bacteria swim is key to understanding critical ecological and biological processes, from carbon cycling to infection. Imaging motility by traditional light microscopy is limited by focus depth, requiring cells to be constrained in z. Holographic microscopy offers an instantaneous 3D snapshot of a large sample volume, and is therefore ideal in principle for quantifying unconstrained bacterial motility. However, resolving and tracking individual cells is difficult due to the low amplitude and phase contrast of the cells; the index of refraction of typical bacteria differs from that of water only at the second decimal place. In...

  12. Reliability and Hardware Implementation of Rank Modulation Flash Memory

    Ma, Yanjun; Li, Yue; Kan, Edwin Chihchuan; Bruck, Jehoshua
    We review a novel data representation scheme for NAND flash memory named rank modulation (RM), and discuss its hardware implementation. We show that under the normal threshold voltage (Vth) variations, RM has intrinsic read reliability advantage over conventional multiple-level cells. Test results demonstrating superior reliability using commercial flash chips are reviewed and discussed. We then present a read method based on relative sensing time, which can obtain the rank of all cells in the group in one read cycle. The improvement in reliability and read speed enable similar program-and-verify time in RM as that of conventional MLC flash.

  13. A Deployable Vivaldi-fed Conical Horn Antenna for CubeSats

    Gupta, Arjun; Costantine, J.; Tawk, Y.; Christodoulou, Christos G.; Pellegrino, S.; Sakovsky, M.
    The advent of CubeSats has revolutionized the space research industry. The small physical size and constraints owing to outer space applications present significant challenges for antenna engineers to come up with innovative solutions. This paper presents a novel wide band antenna high gain antenna which is capable of deploying from a CubeSat platform.

  14. Advanced Conformal Parylene Fabrication for Micro/nano Devices

    Wang, Wei; Liu, Yaoping; Kang, Dongyang; Zhang, Lingqian; Tai, Yu-Chong
    Herein, we reported several advanced parylene fabrication techniques for various micro/nano devices by taking advantages of the conformal deposition capability and overcoming related restrictions when depositing in high aspect ratio structures, including deep-trench filling by Parylene C for thermal isolation in silicon microdevices, parylene molding technique for high porosity filter membrane preparation, Parylene C caulked PDMS (pcPDMS) for low permeability microfluidics applications, and ultra-thin parylene deposition for flexible electronics.

  15. Mars-Moons Exploration, Reconnaissance, and Landed Investigation (MERLIN)

    Murchie, Scott L.; Ehlmann, Bethany L.
    MERLIN, the Mars-Moons Exploration, Reconnaissance and Landed Investigation, is a concept for the first mission to land on the Martian moon Phobos and the first U.S. mission to conduct an in situ investigation of a D-type body typical of the outer solar system. Understanding Phobos and Deimos provides key information for understanding the history and evolution of our solar system and drives MERLIN's combined orbital and landed mission design. MERLIN would perform 9 months of orbital reconnaissance of Phobos and Deimos, characterizing their geology and a landing site on Phobos. Once landed, MERLIN would perform 90 days of complementary measurements...

  16. A computational mechanics avatar for the characterization and analysis of granular matter

    Lim, K.-W.; Kawamoto, R.; Vlahinic, I.; Andrade, J. E.
    We present a computational mechanics avatar that enables unprecedented characterization and analysis of real granular systems. We describe new developments of the avatar framework in the following areas: seamless integration of volumetric data from X-Ray Computed Tomography (XRCT) and discrete element models, and new algorithms for the representation of non-convex particles and implicit time integration. We also present an application of the avatar concept within a multi-scale framework where dilatancy is extracted directly from a real microstructure and upscaled into a continuum finite element model. We shall give an outlook on the future of the avatar concept and discuss its...

  17. Period Estimation and Tracking: Filter Bank Design Using Truth Tables of Logic

    Tenneti, Srikanth V.; Vaidyanathan, P. P.
    Recently, a new filter-bank known as the Ramanujan Filter Bank (RFB) was proposed to detect, estimate and track periodic behavior in data, with several advantages over the traditional methods. Apart from period estimation, the RFB can determine if a given periodic signal is actually a sum of multiple periodic signals with smaller periods. But if one is only interested in period estimation, it is shown in this paper that filter- banks with far fewer filters than the RFB can be designed. These new designs use ideas from digital logic analysis to substantially reduce the number of filters in the RFB.

  18. Minimal Dictionaries For Spanning Periodic Signals

    Tenneti, Srikanth V.; Vaidyanathan, P. P.
    Recently, several high dimensional dictionary representations were proposed for discrete time periodic signals. These dictionaries could span any periodic signal whose period lies in a given range 1 ≤ P ≤ P_(max). Such dictionaries were used in various ways to estimate unknown periods. In this work, we derive some fundamental properties that any such dictionary must satisfy. For example, we derive bounds on the minimum size of such dictionaries, necessary conditions on their composition, and so on. Our results also demonstrate a natural connection between the well-known Euler Totient function (φ-function) from number theory, and periodicity analysis.

  19. On the Fundamental Limits of Caching in Combination Networks

    Ji, Mingyue; Wong, Ming Fai; Tulino, Antonia M.; Llorca, Jaime; Caire, Giuseppe; Effros, Michelle; Langberg, Michael
    The capacity of caching networks has received considerable attention in the past few years. The problem consists of finding the minimum rate (or load) to deliver all users' requested messages from the sources and/or caches in the network. In particular, the capacity of two network models, shared link caching networks and device-to-device caching networks, is relatively well understood. To advance the understanding of the capacity of more general caching networks, in this paper, we study a class of networks of increasing practical interest, namely, the combination caching networks. These networks are formed by a single source connected to n =...

  20. Local Voltage Control in Distribution Systems: An Incremental Control Algorithm

    Farivar, Masoud; Zho, Xinyang; Chen, Lijun
    Inverter-based local volt/var control forms a closed-loop dynamical system whereby the measured voltage determines the reactive power injection, which in turn affects the voltage. There has been only a limited rigorous treatment of the equilibrium and dynamical properties of such feedback systems. In this paper, we expand on our prior result that reverse-engineers a class of non-incremental voltage control schemes and provides a principled way to rigorously engineer the control to incorporate new design goals and/or achieve better dynamical properties. Specifically, it has been observed in the literature that in practical circumstances the droop-based control scheme, a commonly adopted non-incremental...

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