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Caltech Authors (170.931 recursos)

Repository of works by Caltech published authors.

Group = GALCIT

Mostrando recursos 1 - 20 de 445

  1. Optimizing the structure and movement of a robotic bat with biological kinematic synergies

    Hoff, Jonathan; Ramezani, Alireza; Chung, Soon-Jo; Hutchinson, Seth
    In this paper, we present methods to optimize the design and flight characteristics of a biologically-inspired bat-like robot. In previous, work we have designed the topological structure for the wing kinematics of this robot; here we present methods to optimize the geometry of this structure, and to compute actuator trajectories such that its wingbeat pattern closely matches biological counterparts. Our approach is motivated by recent studies on biological bat flight which have shown that the salient aspects of wing motion can be accurately represented in a low-dimensional space. Although bats have over 40 Degrees of Freedom (DoFs), our robot possesses...

  2. A cohesive model of fatigue of ferroelectric materials under electro-mechanical cyclic loading

    Arias, I.; Serebrinsky, S.; Ortiz, M.
    A cohesive fatigue-crack nucleation and growth model for ferroelectric materials under electro-mechanical loading is presented. The central feature of the model is a hysteretic cohesive law which couples the mechanical and electrical fields. This law can be used in conjunction with general constitutive relations of bulk behavior, possibly including domain switching, in order to predict fatigue crack growth under arbitrary loading conditions. Another appealing feature of the model is its ability to predict fatigue-crack nucleation. Despite the scarcity and uncertainty of the experimental data, comparisons with PZT fatigue-life data are encouraging.

  3. Distributed Control Of An Evolving Satellite Assembly During In-Orbit Construction

    Foust, Rebecca C.; Zhao, Michelle; Oliver, Suzanne; Chung, Soon-Jo; Hadaegh, Fred Y.
    This paper presents a method for controlling sets of docked satellites during in-orbit construction of a large-scale satellite assembly from a swarm of heterogeneous satellites. Such a system can be used to enable missions from sparse aperture telescopes to elaborate space stations. Once two or more agents from the swarm are docked, the resulting assembly is an over-actuated system so position and attitude controllers must determine which of the available actuators to use. Typically, control allocation for over-actuated systems is done using a simple linear program, but for this scheme the mass properties and number of control points changes. As...

  4. Distributed Bayesian Filtering using Logarithmic Opinion Pool for Dynamic Sensor Networks

    Bandyopadhyay, Saptarshi; Chung, Soon-Jo
    The discrete-time Distributed Bayesian Filtering (DBF) algorithm is presented for the problem of tracking a target dynamic model using a time-varying network of heterogeneous sensing agents. In the DBF algorithm, the sensing agents combine their normalized likelihood functions in a distributed manner using the logarithmic opinion pool and the dynamic average consensus algorithm. We show that each agent's estimated likelihood function globally exponentially converges to an error ball centered on the joint likelihood function of the centralized multi-sensor Bayesian filtering algorithm. We rigorously characterize the convergence, stability, and robustness properties of the DBF algorithm. Moreover, we provide an explicit bound...

  5. The Visual–Inertial Canoe Dataset

    Miller, Martin; Chung, Soon-Jo; Hutchinson, Seth
    We present a dataset collected from a canoe along the Sangamon River in Illinois. The canoe was equipped with a stereo camera, an inertial measurement unit (IMU), and a global positioning system (GPS) device, which provide visual data suitable for stereo or monocular applications, inertial measurements, and position data for ground truth. We recorded a canoe trip up and down the river for 44 minutes covering a 2.7 km round trip. The dataset adds to those previously recorded in unstructured environments and is unique in that it is recorded on a river, which provides its own set of challenges and...

  6. Robotic Herding of a Flock of Birds Using an Unmanned Aerial Vehicle

    Paranjape, Aditya A.; Chung, Soon-Jo; Kim, Kyunam; Shim, D. Hyunchul
    In this paper, we derive an algorithm for enabling a single robotic unmanned aerial vehicle to herd a flock of birds away from a designated volume of space, such as the air space around an airport. The herding algorithm, referred to as the m-waypoint algorithm, is designed using a dynamic model of bird flocking based on Reynolds’ rules. We derive bounds on its performance using a combination of reduced-order modeling of the flock’s motion, heuristics, and rigorous analysis. A unique contribution of our work is the experimental demonstration of several facets of the herding algorithm on flocks of live birds...

  7. Nonlinear Attitude Control of a Spacecraft with Distributed Actuation of Solar Arrays

    Nakka, Yashwanth Kumar; Chung, Soon-Jo; Allison, James T.; Aldrich, Jack B.; Alvarez-Salazar, Oscar S.
    This article presents a novel control architecture and algorithm for precision attitude control of a one-degree-of-freedom dynamic model of a spacecraft. To achieve a parametric model-based control design approach for this new spacecraft actuation and control architecture, the nonlinear dynamics of the open-loop plant are modeled as an Ordinary Differential Equation (ODE)-Partial Differential Equation (PDE) system. The ODE describes the spacecraft single-axis rigid-body rotation, and the PDE describes the spatially continuous flexible dynamics of the solar array including an allocation for a multi-input distributed piezoelectric actuation system bonded on the solar array. This distributed actuation system is called strain-actuated solar...

  8. Strength of tantalum shocked at ultrahigh pressures

    Stebner, Aaron P.; Wehrenberg, Christopher; Li, Bo; Randall, Greg C.; John, Kristen; Hudish, Grant A.; Maddox, Brian; Farrell, Michael; Park, Hye-Sook; Remington, Bruce; Ortiz, Michael; Ravichandran, G.
    High purity polycrystalline tantalum (Ta) was shocked through 1 to 3.5 Mbar pressures creating Richtmyer-Meshkov unstable interfaces that were used to determine the dynamic material strength. The experiments were performed on the Omega laser at the University of Rochester Laboratory for Laser Energetics. Prior to shock, the driven surfaces of the tantalum targets where coined with a sinusoidal pattern. The targets were recovered post-shock, and the growth of the sinusoid amplitudes was used to characterize the relative extent of plastic deformation as a function of laser energy. Analogous data were extracted prior to the experiments from phenomenological Von Mises plasticity...

  9. Heterodyne diffracted beam photonic Doppler velocimeter (DPDV) for measurement of transverse and normal particle velocities in pressure-shear plate impact experiments

    Mello, Michael; Kettenbeil, Christian; Bischann, Moriah; Ravichandran, Guruswami
    Pressure-shear plate impact (PSPI) experiments have traditionally relied on free space beam interferometers such as the transverse displacement interferometer (TDI) and normal displacement interferometer (NDI) or normal velocity interferometer (NVI), to measure transverse and normal velocities at the rear surface of the target plate [1]. Alternative interferometer schemes feature a dual beam VISAR arrangement [2] and a recently developed all fiber-optic TDI-NDI/PDV configuration [3]. Here, we present a heterodyne diffracted beam PDV (DPDV) which interferes a pair of symmetrically diffracted 1st order beams produced by a thin, specular, metallic grating deposited on the rear surface of the target plate. Each...

  10. Experimental investigation of the shearing resistance of SODA-Lime glass at pressures of 9 GPa and strain rates of 10^6 s^(-1)

    Jiao, T.; Kettenbeil, C.; Ravichandran, G.; Clifton, R. J.
    Pressure-Shear Plate Impact (PSPI) experiments were conducted to measure the high-rate shearing resistance of soda-lime glass at pressures of 9 GPa and at shearing rates of approximately 10^6 s^(−1). Samples of soda lime glass, 5 µm thick, were sandwiched between pure tungsten carbide (WC) plates and impacted by pure WC flyers. Impacting plates were inclined to the direction of approach by an angle of 18°. Normal stress and shearing resistance of the sample were calculated from measured free surface velocities using 1D elastic wave theory. The experimental results show that, at a pressure of 9GPa, the shear stress increases almost linearly up...

  11. Pressure-shear plate impact experiment on soda-lime glass at a pressure of 30 GPa and strain rate of 4·10^7 s^(-1)

    Kettenbeil, Christian; Mello, Michael; Jiao, Tong; Clifton, Rodney J.; Ravichandran, Guruswami
    Recent modifications of a powder gun facility at Caltech have enabled pressure-shear plate impact (PSPI) experiments in a regime of pressures and strain rates that were previously unaccessible. A novel heterodyne diffracted beam photonic Doppler velocimeter (DPDV) has also been developed for simultaneous measurement of the normal and transverse particle velocity histories using the ±1st order diffracted beams produced by a 400 lines/mm diffraction grating deposited onto the polished rear surface of the impacted target plate. We present and interpret the results of a PSPI experiment conducted on a 5 µm thick soda-lime glass sample subjected to a normal stress...

  12. Dynamic Roughness for Manipulation and Control of Turbulent Boundary Layers: An Overview

    McKeon, Beverley J.; Jacobi, Ian; Duvvuri, Subrahmanyam
    The use of dynamic roughness or small, oscillating, wall roughness elements to manipulate the structure of turbulent boundary layers is reviewed with a view to imposing true active control techniques. Linear and nonlinear responses to simple oscillations are detailed, such that the modifications of the overall structure of the turbulence and interactions between scales can be inferred. Although the work considered here uses mechanical actuation, the approach is considered sufficiently general to be implemented by a range of techniques, including engineered microelectromechanical system devices and metamaterial actuators.

  13. Accuracy of a Novel Handheld Wireless Platform for Detection of Cardiac Dysfunction in Anthracycline-Exposed Survivors of Childhood Cancer

    Armenian, Saro H.; Rinderknecht, Derek; Au, Kaylene; Lindenfeld, Lanie; Mills, George; Siyahian, Aida; Herrera, Claudia; Wilson, Karla; Venkataraman, Kalyanasundaram; Mascarenhas, Kristen; Tavallali, Peyman; Razavi, Marianne; Pahlevan, Niema; Detterich, Jon; Bhatia, Smita; Gharib, Morteza
    Childhood cancer survivors are at risk for anthracycline-related cardiac dysfunction, often developing at a time when they are least engaged in long-term survivorship care. New paradigms in survivorship care and chronic disease screening are needed in this population. We compared the accuracy of a novel handheld mHealth platform (Vivio) as well as echocardiography for assessment of cardiac function [left ventricular ejection fraction (EF)] in childhood cancer survivors with cardiac magnetic resonance (CMR) imaging (reference). Cross-sectional study design was used. Concurrent evaluation of EF was performed using Vivio, two-dimensional (2D) echocardiography, and CMR. Differences in mean EF (2D echocardiography vs. CMR;...

  14. Fast and broadband detector for laser radiation

    Scorticati, Davide; Crapella, Giacomo; Pellegrino, Sergio
    We developed a fast detector (patent pending) based on the Laser Induced Transverse Voltage (LITV) effect. The advantage of detectors using the LITV effect over pyroelectric sensors and photodiodes for laser radiation measurements is the combination of an overall fast response time, broadband spectral acceptance, high saturation threshold to direct laser irradiation and the possibility to measure pulsed as well as cw-laser sources. The detector is capable of measuring the energy of single laser pulses with repetition frequencies up to the MHz range, adding the possibility to also measure the output power of cw-lasers. Moreover, the thermal nature of the...

  15. Phenomenological model for coupled multi-axial piezoelectricity

    Wei, Yuchen; Pellegrino, Sergio
    A quantitative calibration of an existing phenomenological model for polycrystalline ferroelectric ceramics is presented. The model relies on remnant strain and polarization as independent variables. Innovative experimental and numerical model identification procedures are developed for the characterization of the coupled electro-mechanical, multi-axial nonlinear constitutive law. Experiments were conducted on thin PZT-5A4E plates subjected to cross-thickness electric field. Unimorph structures with different thickness ratios between PZT-5A4E plate and substrate were tested, to subject the piezo plates to coupled electro-mechanical fields. Material state histories in electric field-strain-polarization space and stress-strain-polarization space were recorded. An optimization procedure is employed for the determination of...

  16. Hypervelocity Impact Flash and Plasma on Electrically Biased Spacecraft Surfaces

    Hew, Y. M.; Goel, A.; Close, S.; Lee, N.
    Hypervelocity microparticles ( < 1 μg), traveling at speeds between 11 and 72 km/s with respect to the Earth, can impact spacecraft and form a small( ∼ 1 μm) and dense ( ∼ 10^(23) m^(−3)) plasma. This plasma can generate a strong optical emission (impact flash) and electromagnetic pulse (EMP), which can lead to spacecraft electrical anomalies when the impacted spacecraft surface carries electrical potential due to various space weather effects. A parameter of the impact plasma that strongly determines its behavior is its temperature. In order to understand the microparticle hypervelocity impact plasma and their associated threat to spacecraft electronics, we need to determine the...

  17. Quantum-well-laser mirror degradation investigated by microprobe optical spectroscopy

    Corvasce, C.; Spagnolo, V.; Scamarcio, G.; Lugarà, M.; Adduci, F.; Ferrara, M.; Sibilano, M.; Pellegrino, S.; Del Guidice, M.; Re, M. G.
    A study of facet degradation of InGaAs quantum well lasers is reported. We tune up a Raman and photoluminescence micro-probe technique for determining the crystal structure and the temperature profile of the cladding layer, in steps of approximately 1 micrometer, with a temperature resolution better than 1 degree Kelvin. The cladding layer composition and cross- section temperature profile have been monitored during operation. A clear correlation between the facet degradation and the type of protective coating is found.

  18. Design of Al-free and Al-based InGaAs/GaAs strained quantum well 980-nm pump lasers including thermal behavior effects on E/O characteristics

    Pellegrino, S.; Re, M. G.; Beoni, C.; Reichenbach, D.; Vidimari, F.
    A 2D thermal simulator and a model to evaluate high power lasers characteristics have been developed. With these models it was possible to optimize cavity length of InGaAs/GaAs (Multiple) Quantum Well 980 nm lasers realized both with Al-based and Al-free confining layers. A comprehensive experimental investigation of the influence of cavity length and temperature on the laser emission wavelength has been performed. This allows a fine trimming of the devices to match the Erbium doped fiber absorption bandwidth.

  19. Design of high-power ridge waveguide 980-nm pump lasers

    Goano, M.; Torasso, E.; Montrosset, I.; Pellegrino, S.; Re, M.; Reichenbach, D.
    The design of ridge waveguide semiconductor pump lasers poses particular simulation problems, since an accurate modeling of the electric and thermal effects and of the optical guiding capabilities is needed. We developed a model whose self-consistent application allows the evaluation of, among others, the threshold current of the lasing mode and the gain margin of the higher order modes, the P-I characteristic, the power coupled in the fiber, and the far field pattern. Particular attention is paid to the experimental verification of the transverse single mode operation region, and its evolution at high injection levels. The appropriate conditions for operation...

  20. Disordering of InGaAs/GaAs strained quantum well structures induced by rare gas ion implantation

    Pellegrino, S.; Pignataro, C.; Caldironi, M.; Dellagiovanna, M.; Vidimari, F.; Carnera, A.; Gasparotto, A.
    In this work we have investigated the effect of various implantation schemes on In(0.2)GaAs/GaAs/AlGaAs Single Quantum Well, where the implanted species are Argon and Helium, with doses in the range 1E12 to 1E14 at cm^2, at energy spanning 270 - 400 KeV and 30 to 50 KeV for Ar and He, respectively. Repetitive annealing processes were carried out between 735 and 870 degree(s)C and the interdiffusion was deduced by photoluminescence measurements. A maximum of 20 nm shift from He ion implanted Quantum Well with an high degree of reconstruction has been recorded, thus allowing the application of this disordering scheme...

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