Recursos de colección

Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 7.506

  1. Equivalence of Sobolev inequalities and Lieb-Thirring inequalities

    Frank, Rupert L.; Lieb, Elliott H.; Seiringer, Robert
    We show that, under very general definitions of a kinetic energy operator T, the Lieb–Thirring inequalities for sums of eigenvalues of T - V can be derived from the Sobolev inequality appropriate to that choice of T.

  2. A sharp bound on eigenvalues of Schröedinger operators on the half-line with complex-valued potentials

    Frank, Rupert L.; Laptev, Ari; Seiringer, Robert
    We derive a sharp bound on the location of non-positive eigenvalues of Schröedinger operators on the halfline with complex-valued potentials.

  3. Capacity of Two-Layer Networks with Binary Weights

    Ji, Chuanyi; Psaltis, Demetri
    The capacity C_b of two later (N - 2L - 1) feed-forward neural networks is shown to satisfy the relation O(W/(lnW)) ≤ C ≤ O(W). Here N - 2L - 1 stands for the networks with N input units, 2L hidden units and one output unit. W is the total number of weights of the networks. The weights take only binary values and the hidden units have integer thresholds.

  4. Mobility of bodies in contact - II: How forces are generated by curvature effects?

    Rimon, Elon; Burdick, Joel
    We investigate the contact forces generated by 2nd order effects for a body B, in frictionless contact with finger bodies A_1,..., A_k. A simple paradox shows that rigid body models are inadequate to explain how contact forces are generated by 2nd order effects. A class of configuration-space based elastic deformation models are introduced, and are shown to explain the restraining forces produced by surface curvature. Using these elastic deformation models, we prove that any object which is kinematically immobilized to 1st or 2nd order is also dynamically locally asymptotically stable with respect to perturbations.

  5. Mobility of bodies in contact - I: A new 2nd order mobility index for multiple-finger grasps

    Rimon, Elon; Burdick, Joel
    Using a configuration-space approach, this paper develops a coordinate invariant 2nd order mobility index for a body, B, in frictionless contact with finger bodies A_1, ..., A_k. The index captures the inherent mobility of B in an equilibrium grasp due to 2nd order, or surface curvature, effects. It differentiates between grasps which are deemed equivalent by the classical 1st order theories, but are physically different. In a companion paper we discuss applications and provide physical justification for using 2nd order immobility effects.

  6. Comparison Of Si/CMOS And GaAs MESFET Technologies For Analog Optoelectronic Circuits

    Grot, Annette C.; Psaltis, Demetri; Shenoy, Krishna V.; Fonstad, Clifton G., Jr.
    We investigate the feasibility of transferring analog optoelectronic circuits designed for Si/CMOS to GaAs and show results of a specific, circuit, originally designed for Si/CMOS, but now fabricated in GaAs.

  7. A Micromachined Permalloy Magnetic Actuator Array for Micro Robotics Assembly Systems

    Liu, Chang; Tsao, Thomas; Tai, Yu-Chong; Liu, Wenheng; Will, Peter; Ho, Chih-Ming
    Arrays of permalloy magnetic actuators have been studied for the use as precision micro robotics assembly systems. The actuator arrays have been tested for lifting and moving silicon and glass chips. The actuator unit consists of a permalloy plate 1 mm x 1 mm X 5µm in size together with polysilicon bending supports. Experimentally, it can lift a 87 µN (or 8.88 mg) force under a magnetic field of approximately 2 x 10^4 A/m. A proposed synchronous driving mode has been observed, and both translation and rotation of a silicon chip has been demonstrated.

  8. Retinomorphic Vision Systems II: Communication Channel Design

    Boahen, Kwabena
    I discuss the tradeoffs faced when asynchronous pulse trains are transmitted among large, two-dimensional, arrays of neurons on different chips, using time-division multiplexing, and present an implementation of an arbitered, random-access, channel. The long cycle time that plagues arbitered channels is addressed in the implementation described here by pipelining. Cycle times ranging from 420ns to 730ns were achieved, for 64 x 64 arrays, in a 2µm CMOS process, yielding a peak throughput of 2.38M spikes/second.

  9. Retinomorphic Vision Systems I: Pixel Design

    Boahen, Kwabena
    I present and analyze test results from circuits that perform all four major operations performed by biological retinae using neurobiological principles: (1) continuous sensing for detection, (2) local automatic gain control for amplification, (3) spatiotemporal bandpass filtering for preprocessing, and (4) adaptive sampling for quantization. In the retinomorphic system that I describe, all these operations are performed at the pixel level, to eliminate redundancy, to reduce power dissipation, and to make efficient use of the capacity of the output channel.

  10. Gas-phase Silicon Etching With Bromine Trifluoride

    Wang, Xuan-Qi; Yang, Xing; Walsh, Ken; Tai, Yu-Chong
    We report the first study of gas phase silicon micromachining using pure bromine trifluoride (BrF/sub 3/) gas at room temperature. This work includes both the design of a new apparatus and etching characterization. Consistent etching results and high molecular etching efficiency (80%) have been achieved by performing the etching in a controlled pulse mode. This pure gaseous BrF/sub 3/ etching process is isotropic and has a high etch rate with superb selectivity over silicon dioxide (3000:1), silicon nitride (400-800:1) and photoresist (1000:1). Moreover, gaseous BrF/sub 3/ etching has also been demonstrated in surface micromachining process, where silicon nitride channels and...

  11. Special angle cut of potassium niobate crystal for thermal fixing

    Tong, Xiaolin; Yariv, Amnon; Agranat, Aharon
    We investigated the optimal cut of potassium niobate crystals to approach the maximum exponential photorefractive gain coefficient and the highest diffraction efficiency. Volume hologram is thermally fixed in this sample and a significant enhancement of diffraction efficiency is achieved.

  12. On the Link Between Electron Shadowing And Charging Damage

    Hwang, Gyeong S.; Giapis, Konstantinos P.
    Charging and topography evolution simulations during plasma etching of high aspect ratio line-and-space patterns reveal that electron shadowing of the sidewalls critically affects charging damage. Decreasing the degree of electron shadowing by using thinner masks decreases the potentials of the etched features with a concomitant reduction in catastrophic tunneling currents through underlying thin gate oxides. Simultaneously, the potential distribution in the trench changes, significantly perturbing the local ion dynamics which, in turn, cause the notching effect to worsen. Since the latter can be reduced independently by selecting an appropriate etch chemistry, the use of thinner (hard) masks is predicted to...

  13. Modular integrated dynamic holographic memory with refreshed holograms

    Chuang, Ernest; Drolet, Jean-Jacques P.; Barbastathis, George; Psaltis, Demetri
    [no abstract]

  14. Improving the Robustness of Deep Neural Networks via Stability Training

    Zheng, Stephan; Song, Yang; Leung, Thomas; Goodfellow, Ian
    In this paper we address the issue of output instability of deep neural networks: small perturbations in the visual input can significantly distort the feature embeddings and output of a neural network. Such instability affects many deep architectures with state-of-the-art performance on a wide range of computer vision tasks. We present a general stability training method to stabilize deep networks against small input distortions that result from various types of common image processing, such as compression, rescaling, and cropping. We validate our method by stabilizing the state of-the-art Inception architecture [11] against these types of distortions. In addition, we demonstrate...

  15. High-power terahertz emitter for a communication link: The chessboard array

    Rivera-Lavado, Alejandro; Atia-Abdalmalak, Kerlos; Santamaría-Botello, Gabriel; González-Ovejero, David; Carpintero, Guillermo; Segovia-Vargas, Daniel; Cámara-Mayorga, Iván; García-Muñoz, Luis Enrique
    This manuscript proposes a high-power terahertz source that consists on a large amount of coherently driven photomixing THz sources. Each element is placed in the gap of a bow tie antenna. The resulting array defines a chessboard-like layout which maximize the density of devices. This novel concept is validated through full-wave simulations. Experimental considerations are also provided for a prototype manufactured for the 1550 nm window. Measured power level will be shown at the conference.

  16. Antireflective textured silicon optics at millimeter and submillimeter wavelengths

    Jung-Kubiak, Cecile; Sayers, Jack; Hollister, Matthew I.; Bose, Arjun; Yoshida, Hiroshige; Liao, Luke; Wong, Jonathan; Radford, Simon; Chattopadhyay, Goutam; Golwala, Sunil
    Silicon optics with broadband antireflective (AR) treatments are being developed for millimeter and submillimeter-wave applications. Combined photolithography and deep reactive ion etching (DRIE) techniques are used to texture the surfaces of high resistivity, low loss silicon wafers. We report on the design, fabrication, and testing at 250 GHz of single and double layer AR treatments on silicon optics.

  17. Analytical study of free-space coupling of THz radiation for a new radioastronomy receiver concept

    Botello, Gabriel Santamaría; Abdalmalak, Kerlos Atia; Schlecht, Maria-Theresa; González-Ovejero, David; Sedlmeir, Florian; Schwefel, Harald G. L.; Malzer, Stefan; Weber, Heiko; Segovia-Vargas, Daniel; McCarthy, Darragh; Murphy, John Anthony; Döhler, Gottfried H.; García Muñoz, Luis-Enrique
    In this paper, a scheme for coupling free-space THz radiation into a nonlinear whispering-gallery mode (WGM) resonator is presented. The purpose is to detect the weak THz radiation from the cosmic microwave background (CMB) by up-converting the signal into the optical domain via the nonlinearity of the medium. Such high-sensitivity receiver has theoretically shown capabilities towards photon counting at room temperature, however, it is critical to efficiently couple the THz radiation into the resonator. Therefore, by using the Schelkunoff-Waterman method (the so called T-matrix method) we perform an analytical evaluation of two different free-space coupling techniques: a freespace Gaussian beam,...

  18. Computational modeling in design of endovascular Chemofilter device for removing toxins from blood

    Maani, Nazanin; Yee, Daryl; Greer, Julia R.; Nosonovsky, Micheal; Hetts, Steven W.; Rayz, Vitaliy L.
    Intra-arterial chemotherapy delivery (IAC) for treating cancer can lead to significant cardiac toxicity due to the drainage of excess drug to the systemic circulation. A catheter-based Chemofilter device temporarily inserted into the veins downstream of the tumor can remove chemotherapy drugs out of the blood stream right after these drugs have had their effect on the tumor. In this research, computational modeling is used to design the Chemofilter and optimize its hemodynamics performance.

  19. Effect of noise on the power spectrum of passively modelocked lasers

    Eliyahu, Danny; Salvatore, Randal A.; Yariv, Amnon
    Modelocking is a common technique employed to produce ultrashort optical pulses from lasers over a wide range of wavelengths. Actively modelocked lasers, for example, are driven by a stable external frequency reference. In this case the timing fluctuations are related to the modulator signal and can be treated as stationary processes. The theory revealed spectral characteristics that are commonly referred to as a spike and a pair of pedestals, with the spike resulting from a delta-function-like shape at each harmonic owing to the external locking source. One pedestal, or side band, at each harmonic is due to amplitude fluctuations and...

  20. Experimental demonstration of a holographic memory with a surface density of 100 bits/(µm^2)

    Pu, Allen; Psaltis, Demetri
    The next generation compact disc due in early 1997, the Digital-Video-Disc (DVD), will have a capacity of ~6 Gbytes per layer, for a maximum planned capacity of ~20 Gbytes per double-sided disk with two layers on each side. That translates to a surface density of approximately 20 bits/(µm^2) for the four-layered DVD disk. In order for holographic three-dimensional disks to be competitive, we must demonstrate a much higher surface density than the most advanced DVD.

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