Recursos de colección

Caltech Authors (166.781 recursos)

Repository of works by Caltech published authors.

Type = Book Section

Mostrando recursos 1 - 20 de 2.133

  1. Multivariable Phase Tuning Control and its Application to Wavelength Tracking in High-Order Multi-Ring Filters

    Mak, Jason C. C.; Sacher, Wesley D.; Mikkelsen, Jared C.; Poon, Joyce K. S.
    We propose a multivariable controller based on a state-space approach and estimation that only requires a single monitor. The procedure is demonstrated on a tunable silicon 5-ring filter to track the passband to a reference wavelength.

  2. Microresonator Soliton Dual-Comb Spectroscopy

    Yang, Qi-Fan; Suh, Myoung-Gyun; Yang, Ki Youl; Yi, Xu; Vahala, Kerry J.
    Dual-comb spectroscopy is demonstrated using microresonator soliton frequency combs by measuring the absorption spectrum of H^(13)CN in the near-infrared. The results show the potential for a chip-based, high-precision spectroscopic system.

  3. Highly Efficient Excitation of Surface Plasmons Using a Si Gable Tip

    Dewanjee, Arnab; Alam, M. Z.; Aitchison, J. Stewart; Mojahedi, Mo.
    We experimentally demonstrate an integrated silicon gabled tip to excite an SPP mode at 1550 nm wavelength at an Au/SiO_2 interface with 25.5% input to SPP output efficiency which can reach as high as 52%.

  4. The role of difference coarrays in correlation subspaces

    Liu, Chun-Lin; Vaidyanathan, P. P.
    The concept of correlation subspaces was recently introduced in array processing literature by Rahmani and Atia. Given a sensor array, its geometry determines the correlation subspace completely, and the covariance matrix of the array output is constrained in a certain way by the correlation subspace. It has been shown by Rahmani and Atia that this knowledge about the covariance constraint can be exploited to improve the performance of DOA estimators. In this paper, it is shown that there is a simple closed form expression for the basis vectors of the correlation subspace. Thus, computation of this subspace is greatly simplified....

  5. Time estimation for heat diffusion on graphs

    Teke, Oguzhan; Vaidyanathan, P. P.
    This paper studies the estimation of the starting time of a diffusion process from its noisy measurements when there is a single point source located on a known vertex of a graph with unknown starting time. The diffusion process is assumed to be governed by the heat equation. In particular, the Cramer-Rao lower bound (CRLB) for the problem is derived. It is shown that the problem has a larger CRLB for graphs with higher connectivity. Closed form expression of the bound is derived for some graphs. The ML estimator is numerically verified to be unbiased, and achieve the CRLB for...

  6. MUSIC and Ramanujan: MUSIC-like algorithms for integer periods using nested-periodic-subspaces

    Tenneti, Srikanth V.; Vaidyanathan, P. P.
    Can the MUSIC algorithm be used for period estimation? Prior works in this direction were based on modifying the search over the conventional complex-exponentials based pseudospectrum to look for harmonically spaced peaks. For applications where the period of the discrete signal can be well approximated by integers, this paper proposes much simpler integer valued basis functions. It is shown that this new re-formulation of MUSIC not only makes the pseudo-spectrum computation much simpler, but also offers significantly higher accuracy than the conventional techniques, especially for mixtures of periodic signals.

  7. Optical frequency synthesis using a dual-Kerr-microresonator frequency comb

    Briles, T. C.; Drake, T. E.; Spencer, D. T.; Stone, J. R.; Fredrick, C.; Li, Q.; Westly, D. A.; Ilic, R.; Yi, X.; Yang, K.; Vahala, K.; Srinivasan, K.; Diddams, S. A.; Papp, S. B.
    We report a photonic-chip optical-frequency synthesizer using interlocking 1 THz and 22 GHz Kerr microcombs, which provide f-2f self-referencing and a dense comb spanning the C-band, respectively. We demonstrate the optical synthesizer with Hz resolution.

  8. Maximally economic sparse arrays and Cantor arrays

    Liu, Chun-Lin; Vaidyanathan, P. P.
    Sparse arrays, where the sensors are properly placed with nonuniform spacing, are able to resolve more uncorrelated sources than sensors. This ability arises from the property that the difference coarray, defined as the differences between sensor locations, has many more consecutive integers (hole-free) than the number of sensors. In some implementations, it might be preferable that a) the arrays be symmetric, b) that the arrays be maximally economic, that is, each sensor be essential, and c) that the coarray be hole-free. The essentialness property of a sensor means that if it is deleted, then the difference coarray changes. Existing sparse...

  9. Single mode dispersive waves and soliton microcomb dynamics

    Yi, Xu; Yang, Qi-Fan; Zhang, Xueyue; Yang, Ki Youl; Vahala, Kerry
    Dispersive-wave scattering from dissipative Kerr solitons is induced by spatial-mode interactions within a high-Q micro-resonator. A limiting case, single-mode dispersive waves, are observed and their interaction with the soliton causes hysteretic behavior.

  10. Atomistic Simulation of Hydrogen Diffusion in Palladium Nanoparticles Using a Diffusive Molecular Dynamics Method

    Sun, Xingsheng; Ariza, Pilar; Ortiz, Michael; Wang, Kevin G.
    Understanding the transport of hydrogen within metals is crucial for the advancement of energy storage and the mitigation of hydrogen embrittlement. Using nanosized palladium particles as a model, recent experimental studies have revealed several highly nonlinear phenomena that occur over a long period of time. The time scale of these phenomena is beyond the capability of established atomistic models. In this work, we present the application of a new model, referred to as diffusive molecular dynamics (DMD), to simulating long-term diffusive mass transport at atomistic length scale. Specifically, we validate the model for the long-term dynamics of a single hydrogen...

  11. Semiconductor Interfaces

    Tan, Ming X.; Bansal, Ashish; Lauermann, Iver; Shreve, Gary A.; Lewis, Nathan S.
    This article describes the properties of semiconductors that are responsible for the operation of rectifiers, transistors, photovoltaic devices, and light emitting. The penetration of the electric field and the electric potential into a bulk semiconductor phase yields a nonuniform carrier concentration in the sample, and produces contacts that either attract or repel specific types of charge carriers. Chemical control over these electric fields is crucial to the technology of semiconductor contacts. In principle, such control can be established through a simple variation in the electrochemical potential of the contacting phase. In practice, this ideal model often does not apply, and...

  12. Metals, Microbes, and Solar Fuel

    Gray, Harry B.; Magyar, John S.
    [no abstract]

  13. Semiconductor Photoelectrochemistry

    Anz, Samir J.; Fajardo, Arnel M.; Royea, William J.; Lewis, Nathan S.; Morris, Amanda J.
    This article discusses methods and experimental protocols in semiconductor electrochemistry. We first discuss the basic principles that govern the energetics and kinetics of charge flow at a semiconductor‐liquid contact. The principal electrochemical techniques of photocurrent and photovoltage measurements used to obtain important interfacial energetic and kinetic quantities of such contacts are then described in detail. After this basic description of concepts and methods in semiconductor electrochemistry, we describe methods for characterizing the optical, electrical, and chemical properties of semiconductors through use of the electrochemical properties of semiconductor‐liquid interfaces.

  14. The Kinetics of TiO_2-based Solar Cells Sensitized by Metal Complexes

    Fitch, Anthony G.; Walker, Don; Lewis, Nathan S.
    [no abstract]

  15. Protein Folding, Misfolding, and Disease

    Lee, Jennifer C.; Kim, Judy E.; Pletneva, Ekaterina V.; Faraone-Mennella, Jasmin; Gray, Harry B.; Winkler, Jay R.
    [no abstract]

  16. Electron Transfer through Proteins

    Winkler, Jay R.; Gray, Harry B.; Prytkova, Tatiana R.; Kurnikov, Igor V.; Beratan, David N.
    [no abstract]

  17. Semiconductors

    Stanton, Colby E.; Nguyen, SonBinh T.; Kesselman, Janet M.; Laibinis, Paul E.; Lewis, Nathan S.
    The structural, electronic, optical, and electrical properties of semiconductors are treated within a common framework. The bonding in the lattice determines the band structure of the solid, which is used to describe the chemical, optical, and electrical properties of the semiconductor. These concepts enable this process to be understood from a qualitative, chemically based viewpoint.

  18. Long-Range Electron Transfer in Biology

    Winkler, Jay R.
    Electron‐transfer processes are vital elements of energy transduction pathways in living cells. A unique synergy between theory and experiment has produced an extraordinarily detailed understanding of the factors that regulate this ‘current of life’. Studies of Ru‐modified proteins have provided insights into the distance‐ and driving‐force dependences of intraprotein electron transfer rates. Electron transfer across protein–protein interfaces has been probed both in solution and in structurally characterized crystals. It is now clear that electrons tunnel between sites in biological redox chains, and that protein structures tune thermodynamic properties and electronic coupling interactions to facilitate these reactions. This research has produced...

  19. Electrochemical Activation of Cytochrome P450

    Udit, Andrew K.; Hill, Michael G.; Gray, Harry B.
    This chapter reviews the efforts to develop catalytically competent P450 systems in which a simple electrode replaces NAD(P)H, and in some instances native reductase proteins, in the catalytic cycle. Notably, in evaluating the successes of P450 electrocatalytic methods, there is an important distinction to be made between mammalian and bacterial systems. While some mention of notable mammalian P450 electrocatalytic systems is made, the chapter focuses primarily on bacterial systems and specifically on the NADPH dependent flavocytochrome P450 from Bacillus megaterium (BM3). Harnessing P450 activity for in vitro applications may be most simply accomplished with electrochemical systems utilizing soluble mediators. Protein–surfactant...

  20. Long-Range Electron Transfer in Donor (Spacer) Acceptor Molecules and Proteins

    Bowler, Bruce E.; Raphael, Adrienne L.; Gray, Harry B.
    [no abstract]

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