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Caltech Authors (140.879 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 7.039

  1. The role of strong convexity-concavity in the convergence and robustness of the saddle-point dynamics

    Cherukuri, Ashish; Mallada, Enrique; Low, Steven; Cortés, Jorge
    This paper studies the projected saddle-point dynamics for a twice differentiable convex-concave function, which we term saddle function. The dynamics consists of gradient descent of the saddle function in variables corresponding to convexity and (projected) gradient ascent in variables corresponding to concavity. We provide a novel characterization of the omega-limit set of the trajectories of these dynamics in terms of the diagonal Hessian blocks of the saddle function. Using this characterization, we establish global asymptotic convergence of the dynamics under local strong convexity-concavity of the saddle function. If this property is global, and for the case when the saddle function...

  2. Metrology camera system of prime focus spectrograph for Subaru Telescope

    Wang, Shiang-Yu; Chou, Richard C. Y.; Huang, Pin-Jie; Ling, Hung-Hsu; Karr, Jennifer; Chang, Yin-Chang; Hu, Yen-Shan; Hsu, Shu-Fu; Chen, Hsin-Yo; Gunn, James E.; Reiley, Dan J.; Tamura, Naoyuki; Takato, Naruhisa; Shimono, Atsushi
    The Prime Focus Spectrograph (PFS) is a new optical/near-infrared multi-fiber spectrograph designed for the prime focus of the 8.2m Subaru telescope. PFS will cover a 1.3 degree diameter field with 2394 fibers to complement the imaging capabilities of Hyper SuprimeCam. To retain high throughput, the final positioning accuracy between the fibers and observing targets of PFS is required to be less than 10 microns. The metrology camera system (MCS) serves as the optical encoder of the fiber motors for the configuring of fibers. MCS provides the fiber positions within a 5 microns error over the 45 cm focal plane. The...

  3. Few Nucleon Problems in Astrophysics

    Tombrello, T. A.
    [no abstract]

  4. Modeling the transmission and thermal emission in a pupil image behind the Keck II adaptive optics system

    Arriaga, Pauline; Fitzgerald, Michael P.; Lyke, James E.; Campbell, Randall D.; Wizinowich, Peter L.; Adkins, Sean M.; Matthews, Keith Y.
    The design and performance of astronomical instruments depend critically on the total system throughput as well as the background emission from the sky and instrumental sources. In designing a pupil stop for background- limited imaging, one seeks to balance throughput and background rejection to optimize measurement signal-to-noise ratios. Many sources affect transmission and emission in infrared imaging behind the Keck Observatory’s adaptive optics systems, such as telescope segments, segment gaps, secondary support structure, and AO bench optics. Here we describe an experiment, using the pupil-viewing mode of NIRC2, to image the pupil plane as a function of wavelength. We are...

  5. Thirty Meter Telescope science instruments: a status report

    Simard, Luc; Ellerbroek, Brent; Bhatia, Ravinder; Radovan, Matthew; Chisholm, Eric
    An overview of the current status of the science instruments for the Thirty Meter Telescope is presented. Three first-light instruments as well as a science calibration unit for AO-assisted instruments are under development. Developing instrument collaborations that can design and build these challenging instruments remains an area of intense activity. In addition to the instruments themselves, a preliminary design for a facility cryogenic cooling system based on gaseous helium turbine expanders has been completed. This system can deliver a total of 2.4 kilowatts of cooling power at 65K to the instruments with essentially no vibrations. Finally, the process for developing...

  6. The Zwicky Transient Facility Camera

    Dekany, Richard; Smith, Roger M.; Belicki, Justin; Delacroix, Alexandre; Duggan, Gina; Feeney, Michael; Hale, David; Kaye, Stephen; Milburn, Jennifer; Murphy, Patrick; Porter, Michael; Reiley, Dan; Riddle, Reed; Rodriguez, Hector; Bellm, Eric
    The Zwicky Transient Facility Camera (ZTFC) is a key element of the ZTF Observing System, the integrated system of optoelectromechanical instrumentation tasked to acquire the wide-field, high-cadence time-domain astronomical data at the heart of the Zwicky Transient Facility. The ZTFC consists of a compact cryostat with large vacuum window protecting a mosaic of 16 large, wafer-scale science CCDs and 4 smaller guide/focus CCDs, a sophisticated vacuum interface board which carries data as electrical signals out of the cryostat, an electromechanical window frame for securing externally inserted optical filter selections, and associated cryo-thermal/vacuum system support elements. The ZTFC provides an instantaneous...

  7. NRES: the network of robotic Echelle spectrographs

    Siverd, Robert J.; Brown, Timothy M.; Hygelund, John; Henderson, Todd; Tufts, Joseph R.; Eastman, Jason D.; van Eyken, Julian; Barnes, Stuart
    Las Cumbres Observatory Global Network (LCOGT) is building the Network of Robotic Echelle Spectrographs (NRES), which will consist of six identical, optical (390 - 860 nm) high-precision spectrographs, each fiber-fed simultaneously by up to two 1-meter telescopes and a thorium argon calibration source. We plan to install one at up to 6 observatory sites in the Northern and Southern hemispheres, creating a single, globally-distributed, autonomous spectrograph facility using up to twelve 1-meter telescopes. Simulations suggest we will achieve long-term radial velocity precision of 3 m/s in less than an hour for stars brighter than V = 12. We have been...

  8. The current status of prime focus instrument of Subaru prime focus spectrograph

    Wang, Shiang-Yu; Schwochert, Mark A.; Huang, Pin-Jie; Chen, Hsin-Yo; Kimura, Masahiko; Chou, Richard C. Y.; Chang, Yin-Chang; Hu, Yen-Sang; Ling, Hung-Hsu; Morantz, Chaz N.; Reiley, Dan J.; Mao, Peter; Braun, David F.; Wen, Chih-Yi; Yan, Chi-Hung; Karr, Jennifer; Gunn, James E.; Murray, Graham; Tamura, Naoyuki; Takato, Naruhisa; Shimono, Atsushi; Ferreira, Decio; dos Santos, Leandro Henrique; Souza Oliveira, Ligia; de Oliveira, Antonio Cesar; Souza Marrara, Lucas
    The Prime Focus Spectrograph (PFS) is a new optical/near-infrared multi-fiber spectrograph design for the prime focus of the 8.2m Subaru telescope. PFS will cover 1.3 degree diameter field with 2394 fibers to complement the imaging capability of Hyper SuprimeCam (HSC). The prime focus unit of PFS called Prime Focus Instrument (PFI) provides the interface with the top structure of Subaru telescope and also accommodates the optical bench in which Cobra fiber positioners are located. In addition, the acquisition and guiding cameras (AGCs), the optical fiber positioner system, the cable wrapper, the fiducial fibers, illuminator, and viewer, the field element, and...

  9. The Infrared Imaging Spectrograph (IRIS) for TMT: multi-tiered wavefront measurements and novel mechanical design

    Dunn, Jennifer; Andersen, David; Chapin, Edward; Reshetov, Vlad; Wierzbicki, Ramunas; Herriot, Glen; Chalmer, Dean; Isbrucker, Victor; Larkin, James E.; Moore, Anna M.; Suzuki, Ryuji
    The InfraRed Imaging Spectrograph (IRIS) will be the first light adaptive optics instrument on the Thirty Meter Telescope (TMT). IRIS is being built by a collaboration between Caltech, the University of California, NAOJ and NRC Herzberg. In this paper we present novel aspects of the Support Structure, Rotator and On-Instrument Wavefront Sensor systems being developed at NRC Herzberg. IRIS is suspended from the bottom port of the Narrow Field Infrared Adaptive Optics System (NFIRAOS), and provides its own image de-rotation to compensate for sidereal rotation of the focal plane. This arrangement is a challenge because NFIRAOS is designed to host...

  10. GRIP - Grids with intelligent periphery: Control architectures for Grid2050^π

    Bakken, D.; Bose, A.; Chandy, K. M.; Khargonekar, P. P.; Kuh, A.; Low, S.; von Meier, A.; Poolla, K.; Varaiya, P. P.; Wu, F.
    A distributed control and coordination architecture for integrating inherently variable and uncertain generation is presented. The key idea is to distribute the intelligence into the periphery of the grid. This will allow coordination of generation, storage, and adjustable demand on the distribution side of the system and thus reduce the need to build new transmission facilities to accommodate large amounts of renewable generation.

  11. Polarimetric decomposition analysis of the Deepwater Horizon oil slick using L-band UAVSAR data

    Jones, Cathleen; Minchew, Brent; Holt, Benjamin
    We report here an analysis of the polarization dependence of L-band radar backscatter from the main slick of the Deepwater Horizon oil spill, with specific attention to the utility of polarimetric decomposition analysis for discrimination of oil from clean water and identification of variations in the oil characteristics. For this study we used data collected with the UAVSAR instrument from opposing look directions directly over the main oil slick. We find that both the Cloude-Pottier and Shannon entropy polarimetric decomposition methods offer promise for oil discrimination, with the Shannon entropy method yielding the same information as contained in the Cloude-Pottier...

  12. Generalized geometric mean decomposition and DFE MMSE transceiver design for cyclic prefix systems

    Liu, Chih-Hao; Vaidyanathan, P. P.
    This paper considers the decomposition of a complex matrix as the product of several sets of semi-unitary matrices and upper triangular matrices in iterative manner. The innermost triangular matrix has its diagonal elements equal to the geometric mean of the singular values of the complex matrix. This decomposition, generalized geometric mean decomposition (GGMD), has one order less complexity than the geometric mean decomposition (GMD) if the target matrix is a diagonal matrix. GGMD can be used to design the optimal decision feedback equalizer (DFE) MMSE transceiver for arbitrary multi-input-multi-output (MIMO) channels. The GGMD transceiver shares the same performance as the...

  13. Low complexity generalized geometric mean decomposition and DFE transceiver design

    Liu, Chih-Hao; Vaidyanathan, P. P.
    The complexity of the generalized geometric mean decomposition (GGMD) depends on the GGMD parameters. This paper consider the low complexity GGMD (LCGGMD) which has the least complexity within the class of GGMD. LCGGMD can be used in designing an optimal decision feedback equalizer (DFE) transceiver for a multi-input-multi-output (MIMO) channel. A novel iterative receiver detection algorithm for the receiver is also proposed. A LCGGMD transceiver always has less or equal design and implementation complexity as compared to a GMD DFE minimum mean square error (MMSE) transceiver. For the applications in which the SVDs of the equivalent MIMO channel matrices can...

  14. The role of GTD in optimizing biorthogonal filter banks

    Weng, Ching-Chih; Vaidyanathan, P. P.
    Filter bank optimization for specific input statistics has been of great interest in both theory and practice in many signal processing applications. In this paper we consider biorthogonal GTD (generalized triangular decomposition) filter banks for optimizing the coding gain. We develop some theoretical results for the optimal biorthogonal GTD subband coder. We also show in both theory and numerical simulations that biorthogonal GTD subband coders have superior performance than biorthogonal subband coders, orthonormal GTD subband coders, and orthonormal subband coders. In addition, the uniform bit loading scheme can with no loss of optimality be used in the optimal biorthogonal GTD...

  15. Nonuniform sparse array design for active sensing

    Weng, Ching-Chih; Vaidyanathan, P. P.
    Active sensing using multiple transmitting elements and independent waveforms has recently attracted much attention. Using M transmitting and N receiving elements, one can virtually simulate a physical array of MN elements by the sum co-array. Nonuniform sparse arrays can further be used in active sensing to produce the difference co-array of the given sum co-array with dramatically increased degree of freedom. However, current literature lacks an efficient design method for active sensing with nonuniform sparse arrays. In this paper, we address this problem and propose several systematic construction methods based on some classical results in number theory. By using these...

  16. Ultrathin parylene-C semipermeable membranes for biomedical applications

    Lu, Bo; Liu, Zhao; Tai, Yu-Chong
    We report here an in-depth study of the permeability of ultrathin parylene-C (0.15-0.80 μm thick) by measuring the diffusion coefficients of FITC-dextran molecules with different molecular weights (MW). As a validation, we have successfully demonstrated the application of the ultrathin semipermeable membranes in perfusion cancer cell culture. The results show that, with a combined biocompatibility and good permeability, ultrathin parylene-C can be a promising semipermeable membrane material for biomedical applications.

  17. Convergence of Incentive-Driven Dynamics in Fisher Markets

    Dvijotham, Krishnamurthy; Rabani, Yuval; Schulman, Leonard J.
    In both general equilibrium theory and game theory, the dominant mathematical models rest on a fully rational solution concept in which every player's action is a best-response to the actions of the other players. In both theories there is less agreement on suitable out- of-equilibrium modeling, but one attractive approach is the level k model in which a level 0 player adopts a very simple response to current conditions, a level 1 player best-responds to a model in which others take level 0 actions, and so forth. (This is analogous to k-ply exploration of game trees in AI, and to...

  18. The Expected Norm of a Sum of Independent Random Matrices: An Elementary Approach

    Tropp, Joel A.
    In contemporary applied and computational mathematics, a frequent challenge is to bound the expectation of the spectral norm of a sum of independent random matrices. This quantity is controlled by the norm of the expected square of the random matrix and the expectation of the maximum squared norm achieved by one of the summands; there is also a weak dependence on the dimension of the random matrix. The purpose of this paper is to give a complete, elementary proof of this important inequality.

  19. Herding a Flock of Birds Approaching an Airport Using an Unmanned Aerial Vehicle

    Gade, Shripad; Paranjape, Aditya A.; Chung, Soon-Jo
    The problem of herding a flock of birds is posed in a graph theoretic framework. A novel algorithm, called the n-wavefront algorithm, Is developed for enabling a single unmanned aerial vehicle to herd a flock of birds to a desired point. The technique is applied to the problem of diverting a flock of birds approaching an airport away from a protected zone around the airport. The n-wavefront algorithm is demonstrated in simulation and compared with existing strategies using graph-based metrics.

  20. HST Observations of the Luminous IRAS Source FSC10214+4724: A Gravitationally Lensed Infrared Quasar

    Eisenhardt, P. R.; Armus, L.; Hogg, D. W.; Soifer, B. T.; Neugebauer, G.; Werner, M. W.
    With a redshift of 2.3, the IRAS source FSC 10214+4724 is apparently one of the most luminous objects known in the Universe. We present an image of FSC10214+4724 at 0.8μm obtained with the Hubble Space Telescope WFPC2 Planetary Camera. The source appears as an unresolved (< 0".06) arc 0".7 long, with significant substructure along its length. The center of curvature of the arc is located near an elliptical galaxy 1".18 to the north. An unresolved component 100 times fainter than the arc is clearly detected on the opposite side of this galaxy. The most straightforward interpretation is that FSC 10214+4724...

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