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Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 63.803

  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. Measuring Flux Distributions for Diffusion in the Small-Numbers Limit

    Seitaridou, Effrosyni; Inamdar, Mandar M.; Phillips, Rob; Ghosh, Kingshuk; Dill, Ken
    For the classical diffusion of independent particles, Fick's law gives a well-known relationship between the average flux and the average concentration gradient. What has not yet been explored experimentally, however, is the dynamical distribution of diffusion rates in the limit of small particle numbers. Here, we measure the distribution of diffusional fluxes using a microfluidics device filled with a colloidal suspension of a small number of microspheres. Our experiments show that (1) the flux distribution is accurately described by a Gaussian function; (2) Fick's law, that the average flux is proportional to the particle gradient, holds even for particle gradients...

  3. Mechanistic Investigation of β-Galactosidase-Activated MR Contrast Agents

    Urbanczyk-Pearson, Lauren M.; Femia, Frank J.; Smith, Jeffrey; Parigi, Giacomo; Duimstra, Joseph A.; Eckermann, Amanda L.; Luchinat, Claudio; Meade, Thomas J.
    We report a mechanistic investigation of an isomeric series of β-galactosidase-activated magnetic resonance contrast agents. Our strategy focuses on the synthesis of macrocyclic caged-complexes that coordinatively saturate a chelated lanthanide. Enzyme cleavage of the complex results in an open coordination site available for water that creates a detectable MR contrast agent. The complexes consist of a DO3A Gd(III) chelator modified with a galactopyranose at the N-10 position of the macrocycle. We observed significant differences in relaxometric properties and coordination geometry that can be correlated to subtle variations of the linker between the macrocycle and the galactopyranose. After synthesis and purification...

  4. Elastic-plastic bending of the lithosphere incorporating rock deformation data, with application to the structure of the Hawaiian archipelago

    Hsi-Ping, Liu; Kosloff, Dan
    An elastic-plastic lithosphere bending model incorporating rock deformation data has been developed for computation of flexure profiles at mid-ocean island chains and at the trenches near the plate boundaries. Flexure of the plate is computed by finite-element numerical solution of Von Kármán's equation for large deflection of plates with a nonlinear material behavior. The elastic part of the constitutive relation is derived from seismology (moduli = 90% of the seismic values) while the strain rate-dependent plastic part is derived from dunite deformation data extrapolated to the appropriate geologic loading rates. As an illustration, the amplitude and the wavelength of the...

  5. 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.

  6. A note on low energy scattering for homogeneous long range potentials

    Frank, Rupert L.
    We explicitly calculate the scattering matrix at energy zero for attractive, radial and homogeneous long-range potentials. This proves a conjecture by Derezinski and Skibsted.

  7. Weakly coupled bound states of Pauli operators

    Frank, Rupert L.; Morozov, Sergey; Vugalter, Semjon
    We consider the two-dimensional Pauli operator perturbed by a weakly coupled, attractive potential. We show that besides the eigenvalues arising from the Aharonov-Casher zero modes there are two or one (depending on whether the flux of the magnetic field is integer or not) additional eigenvalues for arbitrarily small coupling and we calculate their asymptotics in the weak coupling limit.

  8. Inequalities between Dirichlet and Neumann eigenvalues on the Heisenberg group

    Frank, Rupert L.; Laptev, Ari
    We prove that for any domain in the Heisenberg group the (k+1)'th Neumann eigenvalue of the sub-Laplacian is strictly less than the k'th Dirichlet eigenvalue. As a byproduct we obtain similar inequalities for the Euclidean Laplacian with a homogeneous magnetic field.

  9. Crossing the several scales of strain-accomplishing mechanisms in the hinterland of the central Andean fold–thrust belt, Bolivia

    McQuarrie, Nadine; Davis, George H.
    Depictions of structures at outcrop, regional and tectonic scales enforce horizontal shortening and vertical thickening as the predominant style of deformation at all scales within the hinterland of the central Andean fold–thrust belt. Outcrop-scale structures document a progression of strain that created: (1) flexural-slip folds, (2) fold flattening via axial-planar cleavage, (3) vertical stretching via boudinage and late-stage faulting and, finally, (4) kink folding. These examples of intraformational deformation are generally concentrated just beyond the tip lines of thrust faults, where fault-propagation folds and related structures are well developed. Fault-propagation folding accommodated the accrual of strain indicated by outcrop-scale structures...

  10. Dark gauge bosons: LHC signatures of non-Abelian kinetic mixing

    Argüelles, Carlos A.; He, Xiao-Gang; Ovanesyan, Grigory; Peng, Tao; Ramsey-Musolf, Michael J.
    We consider non-abelian kinetic mixing between the Standard Model SU(2)_L and a dark sector U(1)′ gauge group associated with the presence of a scalar SU(2)_L triplet. The magnitude of the resulting dark photon coupling ϵ is determined by the ratio of the triplet vacuum expectation value, constrained to by ≲4 GeV by electroweak precision tests, to the scale Λ of the effective theory. The corresponding effective operator Wilson coefficient can be O(1) while accommodating null results for dark photon searches, allowing for a distinctive LHC dark photon phenomenology. After outlining the possible LHC signatures, we illustrate by recasting current ATLAS...

  11. On acoustic wave beaming in two-dimensional structural lattices

    Zelhofer, Alex J.; Kochmann, Dennis M.
    We discuss directional energy flow, often referred to as wave beaming, in two-dimensional periodic truss lattices under infinitesimal harmonic excitation. While the phenomenon of directional wave guiding is well-known and commonly treated in the context of dispersion relations, the theoretical and computational tools to predict beaming are limited, which is why a fundamental understanding for complex lattices is incomplete. Here, we present a new strategy to identify partial band gaps and wave beaming in a simple fashion, covering wide frequency ranges and distinguishing in-plane and out-of-plane vibrational modes in lattices composed of linear elastic Euler-Bernoulli beams. By calculating group velocities...

  12. Experiments on imperfection insensitive axially loaded cylindrical shells

    Ning, Xin; Pellegrino, Sergio
    This paper presents an experimental study of imperfection insensitive composite wavy cylindrical shells subject to axial compression. A fabrication technique for making cylindrical shells with intricate shape of cross-sections has been developed. A photogrammetry technique to measure the geometric imperfections has also been developed. The behavior of the wavy shells under axial compression was predicted through simulations and measured through compression tests. Both the analyses and experiments have confirmed that the wavy shells are imperfection insensitive. Comparisons between the wavy shells and circular shells have also confirmed that introducing optimal symmetry-breaking wavy cross-sections can significantly reduce the imperfection sensitivity and...

  13. The Herschel Orion Protostar Survey: Luminosity and Envelope Evolution

    Fischer, William J.; Megeath, S. Thomas; Furlan, Elise; Ali, Babar; Stutz, Amelia M.; Tobin, John J.; Osorio, Mayra; Stanke, Thomas; Manoj, P.; Poteet, Charles A.; Booker, Joseph J.; Hartmann, Lee; Wilson, Thomas L.; Myers, Philip C.; Watson, Dan M.
    The Herschel Orion Protostar Survey obtained well-sampled 1.2–870 μm spectral energy distributions (SEDs) of over 300 protostars in the Orion molecular clouds, home to most of the young stellar objects (YSOs) in the nearest 500 pc. We plot the bolometric luminosities and temperatures for 330 Orion YSOs, 315 of which have bolometric temperatures characteristic of protostars. The histogram of the bolometric temperature is roughly flat; 29% of the protostars are in Class 0. The median luminosity decreases by a factor of four with increasing bolometric temperature; consequently, the Class 0 protostars are systematically brighter than the Class I protostars, with...

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

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