Recursos de colección

Caltech Authors (158.172 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 1.300

  1. Toward benchmarking locomotion economy across design configurations on the modular robot: AMBER-3M

    Ambrose, Eric; Ma, Wen-Loong; Hubicki, Christian; Ames, Aaron D.
    Making conclusive performance comparisons of bipedal locomotion behaviors can be difficult when working with different robots. This is particularly true in the case of comparing energy economy, which is highly dependent on mechanical, electrical and control components. As a means of limiting these disparities in methodical testing, we built a modular bipedal robot platform, AMBER-3M. Three leg configurations were designed for this purpose: actuated flat foot, rigid point-foot, and compliant point-foot. As a proof of concept for the mechanical, electrical, and algorithmic modularity, we present walking experiments with all three AMBER-3M configurations, using the same control methods and experimental procedures....

  2. Sub-20-K noise temperature LNA for 67–90 GHz frequency band

    Kangaslahti, Pekka; Cleary, Kieran; Kooi, Jacob; Samoska, Lorene; Lai, Richard; Barsky, Michael; Mei, Xiaobing; Sarkozy, Stephen; Varonen, Mikko
    Indium Phosphide MMIC LNAs are enabling new capabilities in instrument development. The development of arrays of hundreds of cryogenically-cooled millimeter wave receivers has previously been challenging, but is now achievable with highly repeatable MMIC processes and advances in cryogenic on-wafer testing of LNAs. We have developed InP HEMT LNA MMICs for the 67–90 GHz frequency band that is the last missing receiver system from the ALMA. These MMICs provided average performance of less than 22.5 K noise temperature over the frequency band and minimum noise temperature of 17.5 K at 72 GHz. These LNAs achieve NT=220K (NF=2.4dB) at 90 GHz...

  3. Cryogenic W-band LNA for ALMA band 2+3 with average noise temperature of 24 K

    Tang, Yulung; Wadefalk, Niklas; Kooi, Jacob W.; Schleeh, Joel; Moschetti, Giuseppe; Nilsson, Per-Åke; Pourkabirian, Arsalan; Cha, Eunjung; Tuzi, Silvia; Grahn, Jan
    A cryogenic low noise amplifier that operates across the E and W-bands, from 65 GHz to 116 GHz, has been developed using 0.1-μm InP HEMT technology. Such wideband performance makes this work suitable for the ALMA telescope where two of its bands, 67–90 GHz of Band 2 and 85–116 GHz of Band 3, can be combined into one. At an ambient temperature of 5.5 K, this W-band LNA demonstrates an average noise temperature of 24.7 K with more than 21 dB gain and +/−3.0 dB gain flatness from 65 GHz to 116 GHz. To the best knowledge of the authors,...

  4. Realizing simultaneous lane keeping and adaptive speed regulation on accessible mobile robot testbeds

    Xu, Xiangru; Waters, Thomas; Pickem, Daniel; Glotfelter, Paul; Egerstedt, Magnus; Tabuada, Paulo; Grizzle, Jessy W.; Ames, Aaron D.
    This paper presents experimental results on novel robot testbeds that allow the evaluation of the simultaneous implementation of adaptive speed regulation and lane keeping in a safe, education-centric, and inexpensive manner. The underlying algorithms are based on a control Lyapunov function for performance, a control barrier function for safety, and a realtime quadratic program for mediating the conflicting demands of performance and safety. The Robotarium used for this work allows students, as well as researchers less experienced with hardware, to experiment with advanced control concepts in a safe and standardized environment.

  5. Proximal-field radiation sensors

    Safaripour, Amirreza; Hashemi, Mohammed Reza M.; Hajimiri, Ali
    Proximal-Field Radiation Sensors (PFRS) are introduced as a new set of tools to enable extraction of far-field radiation properties of integrated antennas from the surface waves inside their dielectric substrates. These sensors allow self-characterization, self-calibration, and self-monitoring of the radiation performance for both printed circuit board (PCB) antennas and integrated circuit (IC) antennas without any need to additional test equipment. In this paper, we explain how these sensors can be implemented and demonstrate how the far-field radiation properties can be determined from them. A PCB prototype consisting of two transmitting patch antennas and four integrated PFRS antennas is fabricated and...

  6. The efficiency of open access in platforms for networked cournot markets

    Pang, John Z. F.; Fu, Hu; Lee, Won I.; Wierman, Adam
    This paper studies how the efficiency of an online platform is impacted by the degree to which access of platform participants is open or controlled. The study is motivated by an emerging trend within platforms to impose increasingly finegrained control over the options available to platform participants. While early online platforms allowed open access, e.g., Ebay allows any seller to interact with any buyer; modern platforms often impose matches directly, e.g., Uber directly matches drivers to riders. This control is performed with the goal of achieving more efficient market outcomes. However, the results in this paper highlight that imposing matches...

  7. A Time Series Model with Qualitative Variables

    Grether, D. M.; Maddala, G. S.
    The literature on time-series analysis has been largely confined to the analysis of time-series data where: (i) The number of observations is large, and (ii) the variables are all observed as continuous variables.

  8. A difference-integral representation of Koornwinder polynomials

    Rains, Eric M.
    We construct new families of (q-) difference and (contour) integral operators having nice actions on Koornwinder's multivariate orthogonal polynomials. We further show that the Koornwinder polynomials can be constructed by suitable sequences of these operators applied to the constant polynomial 1, giving the difference-integral representation of the title. Macdonald's conjectures (as proved by van Diejen and Sahi) for the principal specialization and norm follow immediately, as does a Cauchy-type identity of Mimachi.

  9. On longest increasing subsequences in random permutations

    Odlyzko, A. M.; Rains, E. M.
    The expected value of L_n, the length of the longest increasing subsequence of a random permutation of {1, ... , n}, has been studied extensively. This paper presents the results of both Monte Carlo and exact computations that explore the finer structure of the distribution of L_n. The results suggested that several of the conjectures that had been made about L_n were incorrect, and led to new conjectures, some of which have been proved recently by Jinho Baik, Percy Deift, and Kurt Johansson. In particular, the standard deviation of L_n is of order n^(1/6), contrary to earlier conjectures. This paper also...

  10. Equilibrium, Disequilibrium, and the General Possibility of a Science of Politics

    Fiorina, Morris P.; Shepsle, Kenneth A.
    Perhaps it overstates matters to say that there is a crisis in formal political theory, but it is apparent that much mischief has been caused by a series of theorems that depict the chaotic features of majority-rule voting systems. These theorems, proved elegantly in recent papers by Cohen (1979), McKelvey (1976, 1979) and Schofield (1978), establish that the cyclicity of the majority preference relation is both generic and pervasive. To paraphrase the title of a recent paper by Bell (1978), when majority rule breaks down, it breaks down completely; and it “almost always” breaks down.

  11. Identifying multiple active conformations in the G protein-coupled receptor activation landscape using computational methods

    Dong, Sijia S.; Goddard, William A., III; Abrol, Ravinder
    G protein-coupled receptors (GPCRs) are membrane proteins critical in cellular signaling, making them important targets for therapeutics. The activation of GPCRs is central to their function, requiring multiple conformations of the GPCRs in their activation landscape. To enable rational design of GPCR-targeting drugs, it is essential to obtain the ensemble of atomistic structures of GPCRs along their activation pathways. This is most challenging for structure determination experiments, making it valuable to develop reliable computational structure prediction methods. In particular, since the active-state conformations are higher in energy (less stable) than inactive-state conformations, they are difficult to stabilize. In addition, the...

  12. Flat and conformal optics with dielectric metasurfaces

    Faraon, Andrei; Arbabi, Amir; Kamali, Seyedeh Mahsa; Arbabi, Ehsan; Horie, Yu
    I discuss our dielectric metasurface platform based on high index nano-posts on a low index substrate, and its applications in imaging, dispersion control, retroreflection and conformal optics.

  13. Integrated optomechanical and superconducting quantum circuits

    Painter, Oskar
    I will present recent work at Caltech on the integration of optomechanical crystals for light and sound with electronic superconducting quantum circuits. Utilizing the silicon-on-insulator (SOI) wafer platform, we have made key advances in the fabrication and integration of extremely low loss microwave phonon structures and low loss microwave superconducting resonators of high impedance. These technical advancements offer several intriguing opportunities for quantum information processing and networking with phonons, photons, and electrons in an integrated, wafer-scale platform. The focus of my talk will be on two examples of our efforts in this direction: (i) nonreciprocal photon transport and amplification arising...

  14. Tunable optical response and purcell enhancement of gated plasmonic structures

    Sokhoyan, Ruzan; Shirmanesh, Ghazaleh Kafaie; Lu, Yu-Jung; Thyagarajan, Krishnan; Pala, Ragip A.; Atwater, Harry A.
    We experimentally demonstrate plasmonic nanostructures that enable dynamic electrical control of the phase and/or amplitude of the plane wave reflected from the nanostructures. We also demonstrate dynamically controlled Purcell enhancement of spontaneous emission of InP quantum dots (QDs) coupled to plasmonic heterostructures.

  15. Turbulence, Cost Escalation and Capital Intensity Bias in Defense Contracting

    Terasawa, Katsuaki; Quirk, James; Womer, Keith
    The recent growth of defense expenditures has once more raised public concern about cost overruns on defense contractors. Economists have pointed out that cost overruns are not necessarily bad per se; instead, attention should be directed to the question as to whether the procurement policies of the Department of Defense (DoD) satisfy the criterion of economic efficiency (see Peck and Sherer (1962)). In connection with this, applications of the principal-agent model to defense contracting show that not only do cost plus fixed fee (CPFF) contracts create moral hazard problems, but that in fact so long as contractors are risk averse...

  16. Keynote address III: Recovery of function in major spinal cord injury using learning-guided spinal stimulation

    Burdick, Joel W.
    Approximately 5,000,000 worldwide suffer from a serious spinal cord injury (SCI). Not only do the injured lose the ability to stand and walk (and sometimes move their arms), they suffer from additional injury-induced complications including loss of bladder and bowel control, decreased cardiovascular and pulmonary health, inability to regulate body temperature, and loss of muscle strength and bone density. The totality of the injury and its secondary dysfunctions makes daily activities of living a challenge. Because the median age of SCI in the U.S. is 32 years, SCI individuals amass an additional 1.4–4.2 million in healthcare costs over their lifetimes....

  17. The subgroup structure of finite groups

    Aschbacher, Michael
    [No abstract]

  18. Tracking in a spaghetti bowl: monitoring transactions using footprints

    Anandkumar, Animashree; Bisdikian, Chatschik; Agrawal, Dakshi
    The problem of tracking end-to-end service-level transactions in the absence of instrumentation support is considered. The transaction instances progress through a state-transition model and generate time-stamped footprints on entering each state in the model. The goal is to track individual transactions using these footprints even when the footprints may not contain any tokens uniquely identifying the transaction instances that generated them. Assuming a semi-Markov process model for state transitions, the transaction instances are tracked probabilistically by matching them to the available footprints according to the maximum likelihood (ML) criterion. Under the ML-rule, for a two-state system, it is shown that...

  19. Are You Going to the Party: Depends, Who Else is Coming?: [Learning Hidden Group Dynamics via Conditional Latent Tree Models]

    Arabshahi, Forough; Huang, Furong; Anandkumar, Animashree; Butts, Carter T.; Fitzhugh, Sean M.
    Scalable probabilistic modeling and prediction in high dimensional multivariate time-series, such as dynamic social networks with co-evolving nodes and edges, is a challenging problem, particularly for systems with hidden sources of dependence and/or homogeneity. Here, we address this problem through the discovery of hierarchical latent groups. We introduce a family of Conditional Latent Tree Models (CLTM), in which tree-structured latent variables incorporate the unknown groups. The latent tree itself is conditioned on observed covariates such as seasonality, historical activity, and node attributes. We propose a statistically efficient framework for learning both the hierarchical tree structure and the parameters of the...

  20. Symmetrized Random Permutations

    Baik, Jinho; Rains, Eric M.
    Selecting N random points in a unit square corresponds to selecting a random permutation. By putting 5 types of symmetry restrictions on the points, we obtain subsets of permutations : involutions, signed permutations and signed involutions. We are interested in the statistics of the length of the longest up/right path of random points selections in each symmetry type as the number of points increases to infinity. The limiting distribution functions are expressed in terms of Painlevé II equation. Some of them are Tracy-Widom distributions in random matrix theory, while there are two new classes of distribution functions interpolating GOE and...

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