Recursos de colección

Caltech Authors (128.467 recursos)

Repository of works by Caltech published authors.

Status = Published

Mostrando recursos 1 - 20 de 56.036

  1. The effect of time on optical coating mechanical loss and implications for LIGO-India

    Kinley-Hanlon, Maya; Fair, Hannah M.; Jiffar, Isaac; Newport, Jonathan; Gitelman, Louis; Harry, Gregory; Billingsley, Garilynn; Penn, Steve
    We report on the persistence of mechanical loss with time of ion beam sputtered dielectric coatings made from alternating layers of Ta_2O_5 and SiO_2 deposited onto fused silica substrates. From this, we predict the coating thermal noise in gravitational wave interferometers, after the coated optics have been stored for years. We measured the modal mechanical quality factor, Q, of two coated fused silica samples in 2015. These samples also had their modal Q's measured in 2002. We conclude that storing the coated silica disks for 13 years does not change their mechanical loss and thus the storage of Advanced LIGO...

  2. Efficient microwave to optical photon conversion: an electro-optical realization

    Rueda, Alfredo; Sedlmeir, Florian; Collodo, Michele C.; Vogl, Ulrich; Stiller, Birgit; Schunk, Gerhard; Strekalov, Dmitry V.; Marquardt, Christoph; Fink, Johannes M.; Painter, Oskar; Leuchs, Gerd; Schwefel, Harald G. L.
    Linking classical microwave electrical circuits to the optical telecommunication band is at the core of modern communication. Future quantum information networks will require coherent microwave-to-optical conversion to link electronic quantum processors and memories via low-loss optical telecommunication networks. Efficient conversion can be achieved with electro-optical modulators operating at the single microwave photon level. In the standard electro-optic modulation scheme, this is impossible because both up- and down-converted sidebands are necessarily present. Here, we demonstrate true single-sideband up- or down-conversion in a triply resonant whispering gallery mode resonator by explicitly addressing modes with asymmetric free spectral range. Compared to previous experiments,...

  3. Uniqueness, universality, and homogeneity of the noncommutative Gurarij space

    Lupini, Martino
    We realize the noncommutative Gurarij space NG defined by Oikhberg as the Fraïssé limit of the class of finite-dimensional 1-exact operator spaces. As a consequence we deduce that the noncommutative Gurarij space is unique up to completely isometric isomorphism, homogeneous, and universal among separable 1-exact operator spaces. We also prove that NG is the unique separable nuclear operator space with the property that the canonical triple morphism from the universal TRO to the triple envelope is an isomorphism. We deduce from this fact that NG does not embed completely isometrically into an exact C*-algebra, and it is not completely isometrically...

  4. Kinetic-energy systems, density scaling, and homogeneity relations in density-functional theory

    Chan, Garnet Kin-Lic; Handy, Nicholas C.
    We examine the behavior of the Kohn-Sham kinetic energy T_s[ρ] and the interacting kinetic energy T[ρ] under homogeneous density scaling, ρ(r)→ζρ(r). Using convexity arguments, we derive simple inequalities and scaling constraints for the kinetic energy. We also demonstrate that a recently derived homogeneity relation for the kinetic energy [S. B. Liu and R. G. Parr, Chem. Phys. Lett. 278, 341 (1997)] does not hold in real systems, due to nonsmoothness of the kinetic-energy functional. We carry out a numerical study of the density scaling of T_s[ρ] using ab initio densities, and find it exhibits an effective homogeneity close to 5/3....

  5. Optimized Lieb-Oxford bound for the exchange-correlation energy

    Chan, Garnet Kin-Lic; Handy, Nicholas C.
    Using the ideas of Lieb and Oxford [Int. J. Quantum Chem. 19, 427 (19810], we show that the exchange-correlation energy, and indirect part of the Coulomb energy, are bounded from below by -1.6358∫ρ^(4/3) (x)dx, where ρ(x) is the single-particle density.

  6. Cosmological measurements with general relativistic galaxy correlations

    Raccanelli, Alvise; Montanari, Francesco; Bertacca, Daniele; Doré, Olivier; Durrer, Ruth
    We investigate the cosmological dependence and the constraining power of large-scale galaxy correlations, including all redshift-distortions, wide-angle, lensing and gravitational potential effects on linear scales. We analyze the cosmological information present in the lensing convergence and in the gravitational potential terms describing the so-called ``relativistic effects'', and we find that, while smaller than the information contained in intrinsic galaxy clustering, it is not negligible. We investigate how neglecting them does bias cosmological measurements performed by future spectroscopic and photometric large-scale surveys such as SKA and Euclid. We perform a Fisher analysis using the CLASS code, modified to include scale-dependent galaxy...

  7. NuSTAR reveals the extreme properties of the super-Eddington accreting supermassive black hole in PG 1247+267

    Lanzuisi, G.; Harrison, F. A.; Walton, D. J.
    PG1247+267 is one of the most luminous known quasars at z ~ 2 and is a strongly super-Eddington accreting supermassive black hole (SMBH) candidate. We obtained NuSTAR data of this intriguing source in December 2014 with the aim of studying its high-energy emission, leveraging the broad band covered by the new NuSTAR and the archival XMM-Newton data. Several measurements are in agreement with the super-Eddington scenario for PG1247+267: the soft power law (Γ = 2.3 ± 0.1); the weak ionized Fe emission line; and a hint of the presence of outflowing ionized gas surrounding the SMBH. The presence of an...

  8. The VIPERS Multi-Lambda Survey I. UV and near-IR observations, multi-colour catalogues, and photometric redshifts

    Moutard, T.; Arnouts, S.; Ilbert, O.; Coupon, J.; Hudelot, P.; Vibert, D.; Comte, V.; Conseil, S.; Davidzon, I.; Guzzo, L.; Llebaria, A.; Martin, C.; McCracken, H. J.; Milliard, B.; Morrison, G.; Schiminovich, D.; Treyer, M.; Van Werbaeke, L.
    We present observations collected in the CFHTLS-VIPERS region in the ultraviolet with the GALEX satellite (far- and near-ultraviolet channels) and in the near-infrared with the CFHT/WIRCam camera (K_s band) over an area of 22 and 27 deg^2, respectively. The depth of the photometry was optimised to measure the physical properties (e.g., star formation rate, stellar masses) of all the galaxies in the VIPERS spectroscopic survey. The large volume explored by VIPERS will enable a unique investigation of the relationship between the galaxy properties and their environment (density field and cosmic web) at high redshift (0.5 ≤ z ≤ 1.2). In...

  9. Analysis of the 3DVAR filter for the partially observed Lorenz'63 model

    Law, Kody; Shukla, Abishek; Stuart, Andrew
    The problem of effectively combining data with a mathematical model constitutes a major challenge in applied mathematics. It is particular challenging for high-dimensional dynamical systems where data is received sequentially in time and the objective is to estimate the system state in an on-line fashion; this situation arises, for example, in weather forecasting. The sequential particle filter is then impractical and ad hoc filters, which employ some form of Gaussian approximation, are widely used. Prototypical of these ad hoc filters is the 3DVAR method. The goal of this paper is to analyze the 3DVAR method, using the Lorenz '63 model...

  10. Bayesian posterior contraction rates for linear severely ill-posed inverse problems

    Agapiou, Sergios; Stuart, Andrew M.; Zhang, Yuan-Xiang
    We consider a class of linear ill-posed inverse problems arising from inversion of a compact operator with singular values which decay exponentially to zero. We adopt a Bayesian approach, assuming a Gaussian prior on the unknown function. The observational noise is assumed to be Gaussian; as a consequence the prior is conjugate to the likelihood so that the posterior distribution is also Gaussian. We study Bayesian posterior consistency in the small observational noise limit. We assume that the forward operator and the prior and noise covariance operators commute with one another. We show how, for given smoothness assumptions on the...

  11. Determining white noise forcing from Eulerian observations in the Navier-Stokes equation

    Hoang, Viet Ha; Law, Kody J. H.; Stuart, Andrew M.
    The Bayesian approach to inverse problems is of paramount importance in quantifying uncertainty about the input to, and the state of, a system of interest given noisy observations. Herein we consider the forward problem of the forced 2D Navier-Stokes equation. The inverse problem is to make inference concerning the forcing, and possibly the initial condition, given noisy observations of the velocity field. We place a prior on the forcing which is in the form of a spatially-correlated and temporally-white Gaussian process, and formulate the inverse problem for the posterior distribution. Given appropriate spatial regularity conditions, we show that the solution...

  12. A fresh look at ensembles: Derivative discontinuities in density functional theory

    Chan, Garnet Kin-Lic
    We present a zero temperature ensemble spin density functional theory. We discuss the ensemble quantities that arise from derivative discontinuities, including the nonvanishing asymptotic potential and band gap shift, in the context of the Kohn–Sham formalism, and hybrid exact exchange theories, such as the Hartree–Fock–Kohn–Sham formalism. We describe and implement a general method of calculating these quantities in atomic and molecular systems. Finally we discuss how our results explain the deficiencies of existing functionals, and how new functionals should be constructed, illustrating our conclusions by examining the dissociation of H^(+)_2.

  13. Noisy gradient flow from a random walk in Hilbert space

    Pillai, Natesh S.; Stuart, Andrew M.; Thiéry, Alexandre H.
    Consider a probability measure on a Hilbert space defined via its density with respect to a Gaussian. The purpose of this paper is to demonstrate that an appropriately defined Markov chain, which is reversible with respect to the measure in question, exhibits a diffusion limit to a noisy gradient flow, also reversible with respect to the same measure. The Markov chain is defined by applying a Metropolis–Hastings accept–reject mechanism (Tierney, Ann Appl Probab 8:1–9, 1998) to an Ornstein–Uhlenbeck (OU) proposal which is itself reversible with respect to the underlying Gaussian measure. The resulting noisy gradient flow is a stochastic partial...

  14. Spectral gaps for a Metropolis–Hastings algorithm in infinite dimensions

    Hairer, Martin; Stuart, Andrew M.; Vollmer, Sebastian
    We study the problem of sampling high and infinite dimensional target measures arising in applications such as conditioned diffusions and inverse problems. We focus on those that arise from approximating measures on Hilbert spaces defined via a density with respect to a Gaussian reference measure. We consider the Metropolis–Hastings algorithm that adds an accept–reject mechanism to a Markov chain proposal in order to make the chain reversible with respect to the target measure. We focus on cases where the proposal is either a Gaussian random walk (RWM) with covariance equal to that of the reference measure or an Ornstein–Uhlenbeck proposal...

  15. Well-posedness and accuracy of the ensemble Kalman filter in discrete and continuous time

    Kelly, D. B. T.; Law, K. J. H.; Stuart, A. M.
    The ensemble Kalman filter (EnKF) is a method for combining a dynamical model with data in a sequential fashion. Despite its widespread use, there has been little analysis of its theoretical properties. Many of the algorithmic innovations associated with the filter, which are required to make a useable algorithm in practice, are derived in an ad hoc fashion. The aim of this paper is to initiate the development of a systematic analysis of the EnKF, in particular to do so for small ensemble size. The perspective is to view the method as a state estimator, and not as an algorithm...

  16. Analysis of the Gibbs Sampler for Hierarchical Inverse Problems

    Agapiou, Sergios; Bardsley, Jonathan M.; Papaspiliopoulos, Omiros; Stuart, Andrew M.
    Many inverse problems arising in applications come from continuum models where the unknown parameter is a field. In practice the unknown field is discretized, resulting in a problem in ℝ^N, with an understanding that refining the discretization, that is, increasing N, will often be desirable. In the context of Bayesian inversion this situation suggests the importance of two issues: (i) defining hyperparameters in such a way that they are interpretable in the continuum limit N →∞ and so that their values may be compared between different discretization levels; and (ii) understanding the efficiency of algorithms for probing the posterior distribution...

  17. Well-posed Bayesian geometric inverse problems arising in subsurface flow

    Iglesias, Marco A.; Lin, Kui; Stuart, Andrew M.
    In this paper, we consider the inverse problem of determining the permeability of the subsurface from hydraulic head measurements, within the framework of a steady Darcy model of groundwater flow. We study geometrically defined prior permeability fields, which admit layered, fault and channel structures, in order to mimic realistic subsurface features; within each layer we adopt either a constant or continuous function representation of the permeability. This prior model leads to a parameter identification problem for a finite number of unknown parameters determining the geometry, together with either a finite number of permeability values (in the constant case) or a...

  18. Gerry Neugebauer - 1932–2014

    Soifer, B. Thomas
    Gerry Neugebauer was one of a small band of experimental physicists who used their perspectives to create a new discipline within astrophysics. Together they founded what is now known as infrared astronomy. Gerry’s commitment to innovative instruments and sky surveys exploring the unknown universe was matched by his commitment to the highest quality of published and archived data, which were vital to the creation of a dominant discipline in modern observational astrophysics. His discovery of many new kinds of celestial objects and phenomena, studies of which have remained vibrant subfields of astrophysics to this day, brought many others into the field that he helped invent. Neugebauer did his undergraduate study at Cornell University and...

  19. Characterization of transient noise in Advanced LIGO relevant to gravitational wave signal GW150914

    Abbott, B. P.; Abbott, R.; Abernathy, M. R.; Adhikari, R. X.; Anderson, S. B.; Arai, K.; Araya, M. C.; Barayoga, J. C.; Barish, B. C.; Berger, B. K.; Billingsley, G.; Blackburn, J. K.; Bodiya, T. P.; Bork, R.; Brooks, A. F.; Cahillane, C.; Callister, T.; Cepeda, C. B.; Chakraborty, R.; Chalermsongsak, T.; Couvares, P.; Coyne, D. C.; Dergachev, V.; Drever, R. W. P.; Ehrens, P.; Etzel, T.; Gossan, S. E.; Gushwa, K. E.; Gustafson, E. K.; Hall, E. D.; Heptonstall, A. W.; Hodge, K. A.; Isi, M.; Kanner, J. B.; Kells, W.; Kondrashov, V.; Korth, W. Z.; Kozak, D. B.; Lazzarini, A.; Li, T. G. F.; Mageswaran, M.; Maros, E.; Martynov, D. V.; Marx, J. N.; McIntyre, G.; McIver, J.; Meshkov, S.; Pedraza, M.; Perreca, A.; Price , L. R.; Quintero, E. A.; Reitze, D. H.; Robertson, N. A.; Rollins, J. G.; Sachdev, S.; Sanchez, E. J.; Schmidt, P.; Shao, Z.; Singer, A.; Smith, N. D.; Smith, R. J. E.; Taylor, R.; Thirugnanasambandam, M. P.; Torrie, C. I.; Vajente, G.; Vass, S.; Wallace, L.; Weinstein, A. J.; Whitcomb, S.; Williams, R. D.; Wipf, C. C.; Yamamoto, H.; Zhang, L.; Zucker, M. E.; Zweizig, J.
    On 14 September 2015, a gravitational wave signal from a coalescing black hole binary system was observed by the Advanced LIGO detectors. This paper describes the transient noise backgrounds used to determine the significance of the event (designated GW150914) and presents the results of investigations into potential correlated or uncorrelated sources of transient noise in the detectors around the time of the event. The detectors were operating nominally at the time of GW150914. We have ruled out environmental influences and non-Gaussian instrument noise at either LIGO detector as the cause of the observed gravitational wave signal.

  20. Planet Hunters X: Searching for Nearby Neighbors of 75 Planet and Eclipsing Binary Candidates from the K2 Kepler Extended Mission

    Schmitt, Joseph R.; Tokovinin, Andrei; Wang, Ji; Fischer, Debra A.; Kristiansen, Martti H.; LaCourse, Daryll M.; Gagliano, Robert; Tan, Arvin Joseff V.; Schwengeler, Hans Martin; Omohundro, Mark R.; Venner, Alexander; Terentev, Ivan; Schmitt, Allan R.; Jacobs, Thomas L.; Winarski, Troy; Sejpka, Johann; Jek, Kian J.; Boyajian, Tabetha S.; Brewer, John M.; Ishikawa, Sascha T.; Lintott, Chris; Lynn, Stuart; Schawinski, Kevin; Schwamb, Megan E.; Weiksnar, Alex
    We present high-resolution observations of a sample of 75 K2 targets from Campaigns 1–3 using speckle interferometry on the Southern Astrophysical Research (SOAR) telescope and adaptive optics imaging at the Keck II telescope. The median SOAR I-band and Keck K_s-band detection limits at 1" were Δm_I = 4.4 mag and Δm_K_s = 6.1 mag, respectively. This sample includes 37 stars likely to host planets, 32 targets likely to be eclipsing binaries (EBs), and 6 other targets previously labeled as likely planetary false positives. We find nine likely physically bound companion stars within 3" of three candidate transiting exoplanet host stars...

Aviso de cookies: Usamos cookies propias y de terceros para mejorar nuestros servicios, para análisis estadístico y para mostrarle publicidad. Si continua navegando consideramos que acepta su uso en los términos establecidos en la Política de cookies.