Repository of works by Caltech published authors.
Type = Report or Paper
Mostrando recursos 1 - 20 de 3,216
Overview of Saturn lightning observations - Fischer, G.; Dyudina, U. A.; Kurth, W. S.; Gurnett, D. A.; Zarka, P.; Barry, T.; Delcroix, M.; Go, C.; Peach, D.; Vandebergh, R.; Wesley, A.
The lightning activity in Saturn's atmosphere has been monitored by Cassini for more than six years. The continuous observations of the radio signatures called SEDs (Saturn Electrostatic Discharges) combine favorably with imaging observations of related cloud features as well as direct observations of flash-illuminated cloud tops. The Cassini RPWS (Radio and Plasma Wave Science) instrument and ISS (Imaging Science Subsystem) in orbit around Saturn also received ground-based support: The intense SED radio waves were also detected by the giant UTR-2 radio telescope, and committed amateurs observed SED-related white spots with their backyard optical telescopes. Furthermore, the Cassini VIMS (Visual and...
Reflected Light Curves, Spherical and Bond Albedos of Jupiter- and Saturn-like Exoplanets - Dyudina, Ulyana; Zhang, Xi; Li, Liming; Kopparla, Pushkar; Yung, Yuk L.; Ingersoll, Andrew P.; Dones, Luke
We estimate how the light curve and total stellar heating of a planet depend on forward and backward scattering clouds. To do that, we construct light curves for Jupiter- and Saturn-like planet based on observations. We fit analytical functions to the reflected brightness of Jupiter's and Saturn's surface versus planet's phase. We use Pioneer and Cassini spacecraft images to estimate these functions. These observations cover broad bands at 0.59-0.72 µm and 0.39-0.5 µm, and narrow bands at 0.938 µm (atmospheric window), 0.889 µm (CH_4 absorption band), and 0.24-0.28 µm. We simulate the images of the planets at different phases with...
Nonlinear ordinary difference equations - Caughey, Thomas K.
Future space vehicles will be relatively large and flexible, and active control will be necessary to maintain geometrical configuration. While the stresses and strains in these space vehicles are not expected to be excessively large, their cumulative effects will cause significant geometrical nonlinearities to appear in the equations of motion, in addition to the nonlinearities caused by material properties. Since the only effective tool for the analysis of such large complex structures is the digital computer, it will be necessary to gain a better understanding of the nonlinear ordinary difference equations which result from the time discretization of the semidiscrete...
Apollo Program Soil Mechanics Experiment: Final Report - Scott, R. F.
The Apollo lunar landing missions provided the first opportunity for
direct collection of data relating to the physical characteristics and mechanical
behavior of the surface materials of an extraterrestrial body by
other than remote means. The acquisition of such information from the
first manned lunar landings was needed to aid in accomplishing the following
1. To provide engineering data on the interaction of man and equipment
with the lunar surface, thereby aiding in the evaluation of the Apollo
missions, and in the planning of future lunar surface scientific investigations and related engineering tasks supporting these activities.
2. To enhance the scientific understanding of the nature and origin...
Matrix Perturbation Techniques in Structural Dynamics - Caughey, T. K.
The purpose of the present report is to develop certain matrix
perturbation techniques which can be used in the dynamical analysis
of structures where the range of numerical values in the matrices is
extreme or where the nature of the damping matrix requires that complex
valued eigenvalues and eigenvectors be used. The techniques can be
advantageously used in a variety of fields such as earthquake engineering,
ocean engineering, aerospace engineering and other fields concerned
with the dynamical analysis of large complex structures or systems of
second order differential equations.
A number of simple examples are included to illustrate the
The no-spin zone: rotation vs dispersion support in observed and simulated dwarf galaxies - Wheeler, Coral; Pace, Andrew B.; Bullock, James S.; Boylan-Kolchin, Michael; Oñorbe, José; Fitts, Alex; Hopkins, Philip F.; Kereš, Dušan
We perform a systematic Bayesian analysis of rotation vs. dispersion support (v_(rot)/σ) in 40 dwarf galaxies throughout the Local Volume (LV) over a stellar mass range 10^(3.5) M_⊙ < M⋆ < 10^8 M_⊙. We find that the stars in ∼90% of the LV dwarf galaxies studied -- both satellites and isolated systems -- are dispersion-supported. In particular, we show that 7/10 *isolated* dwarfs in our sample have stellar populations with v_(rot)/σ<0.6. All have v_(rot)/σ≲2. These results challenge the traditional view that the stars in gas-rich dwarf irregulars (dIrrs) are distributed in cold, rotationally-supported stellar disks, while gas-poor dwarf spheroidals (dSphs)...
Herschel HIFI Observations of the Sgr A +50 km s^(-1) Cloud. Deep Searches for O_2 in Emission and Foreground Absorption - Sandqvist, Aa.; Larsson, B.; Hjalmarson, Å.; Encrenaz, P.; Gerin, M.; Goldsmith, P. F.; Lis, D. C.; Liseau, R.; Pagani, L.; Roueff, E.; Viti, S.
Context. The Herschel Oxygen Project (HOP) is an Open Time Key Program, awarded 140 hours of observing time to search for
molecular oxygen (O_2) in a number of interstellar sources. To date O_2 has definitely been detected in only two sources, namely ρ Oph
A and Orion, reflecting the extremely low abundance of O_2 in the interstellar medium.
Aims. One of the sources in the HOP program is the +50 kms^(−1) Cloud in the Sgr A Complex in the centre of the Milky Way. Its
environment is unique in the Galaxy and this property is investigated to see if it is conducive to...
Non-Uniform Flow in Multistage Axial Compressors - Marble, Frank E.
It has been suggested by the author that some aspects of
severely distorted flow into multistage compressors may be examined utilizing an integral technique. The general idea of the proposed technique is clear enough; the appropriate equations of motion and energy are integrated peripherally and radially, using reasonable assumptions for the distributions of velocity and thermodynamic
properties, and thereby reduced to ordinary non-linear differential equations for the parameters that describe the distributions. The questions that arise are whether the cascade characteristics may be described appropriately over wide variations of inlet angle, including stall, and whether the profiles may be characterized by a
Noise Produced by the Interaction of Acoustic Waves and Entropy Waves with High-Speed Nozzle Flows - Bohn, Mark S.
Some aspects of the noise generated internally by a turbojet
engine are considered analytically and experimentally. The emphasis is placed on the interaction of pressure fluctuations and entropy fluctuations,
produced by the combustion process in the engine, with
gradients in the mean flow through the turbine blades or the exhaust nozzle. The results are directly applicable to the problem of excess noise in aircraft powerplants and suggest that the phenomenon described is the dominant mechanism.
The one-dimensional interaction of pressure fluctuations and
entropy fluctuations with a subsonic nozzle is solved analytically. The acoustic waves produced by each of three independent disturbances are investigated. These disturbances,...
Shock Wave Effects on the Laminar Skin Friction of an Insulated Flat Plate at Hypersonic Speeds - Li, Ting-Yi
An approximate theory on the phenomena of interaction between the shock wave and the laminar boundary layer on an insulated flat plate at hypersonic speeds has been formulated. Results on the rate of growth of the boundary layer thickness and the rate of decay of the shock wave strength have been found for M_1^(2(2+w)R_1^-1 = O(1). A new set of formulae for the average skin friction coefficient, C_F, over an insulated flat plate at hypersonic speeds has been obtained. Calculations on the basis of the new C_F formulae yield the data shown in Figs. 5 and 6. Contrary to the...
Next Generation Very Large Array Memo No. 5 Science Working Groups Project Overview - Carilli, C. L.; McKinnon, M.; Ott, J.; Beasley, A.; Isella, A.; Murphy, E.; Leroy, A.; Casey, C.; Moullet, A.; Lacy, M.; Hodge, J.; Bower, G.; Demorest, P.; Hull, C.; Hughes, M.; Di Francesco, J.; Narayanan, D.; Kent, B.; Clark, B.; Butler, B.
We summarize the design, capabilities, and some of the priority science goals of a next generation Very Large Array (ngVLA). The ngVLA is an interferometric array with 10x larger effective collecting area and 10x higher spatial resolution than the current VLA and the Atacama Large Millimeter Array (ALMA), optimized for operation in the wavelength range 0.3cm to 3cm. The ngVLA opens a new window on the Universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcecond resolution, as well as unprecedented broad band continuum polarimetric imaging of non-thermal processes. The continuum resolution will reach 9mas at 1cm,...
ULX behaviour: the ultraluminous state, winds & interesting anomalies - Roberts, T. P.; Middleton, M. J.; Sutton, A. D.; Mezcua, M.; Walton, D. J.; Heil, L. M.
Recent evidence - in particular the hard X-ray spectra obtained by NuSTAR, and the large amplitude hard X-ray variability observed when ultraluminous X-ray sources (ULXs) show soft spectra - reveals that common ULX behaviour is inconsistent with known sub-Eddington accretion modes, as would be expected for an intermediate-mass black hole (IMBH). Instead, it appears that the majority of ULXs are powered by super-Eddington accretion onto stellar-mass black holes. Here, we will review work that delves deeper into ULX spectral-timing behaviour, demonstrating it remains consistent with the expectations of super-Eddington accretion. One critical missing piece from this picture is the direct...
NuSTAR and XMM-Newton Observations of the Hard X-Ray Spectrum of Centaurus A - Fuerst, F.; Müller, C.; Madsen, K. K.; Lanz, L.; Rivers, E.; Brightman, M.; Arevalo, P.; Baloković, M.; Beuchert, T.; Boggs, S. E.; Christensen, F. E.; Craig, W. W.; Dauser, T.; Farrah, D.; Graefe, C.; Hailey, C. J.; Harrison, F. A.; Kadler, M.; King, A.; Krauss, F.; Madejski, G.; Matt, G.; Marinucci, A.; Markowitz, A.; Ogle, P.; Ojha, R.; Rothschild, R.; Stern, D.; Walton, D. J.; Wilms, J.; Zhang, W. W.
We present simultaneous XMM-Newton and NuSTAR observations spanning 3–78 keV of the nearest radio
galaxy, Centaurus A (Cen A), performed during a very high flux state. The accretion geometry around the
central engine in Cen A is still debated, and we investigate possible configurations using detailed X-ray spectral
modeling. NuSTAR imaged the central region of Cen A with subarcminute resolution at X-ray energies above
10 keV for the first time, but finds no evidence for an extended source or other off-nuclear point-sources.
The XMM-Newton and NuSTAR spectra agree well and can be described with an absorbed power-law with
a photon index Γ = 1.815 ± 0.005...
BICEP2 / Keck Array VI: Improved Constraints On Cosmology and Foregrounds When Adding 95 GHz Data From Keck Array - Bock, J.; Brevik, J. A.; Filippini, J. P.; Hui, H.; Kefeli, S.; Lueker, M.; O'Brient, R.; Orlando, A.; Staniszewski, Z. K.; Steinbach, B.; Teply, G. P.
We present results from an analysis of all data taken by the BICEP2 & Keck
Array CMB polarization experiments up to and including that taken during the
2014 observing season. This includes the first Keck Array observations at 95
GHz. The maps reach a depth of 50 nK deg in Stokes Q and U in the 150 GHz
band and 127 nK deg in the 95 GHz band. We take auto- and cross-spectra between
these maps and publicly available maps from WMAP and Planck at frequencies from
23 GHz to 353 GHz. An excess over lensed-LCDM is detected at modest
significance in the 95x150 BB spectrum, and...
An Excess of Mid-Infrared Emission from the Type Iax SN 2014dt - Fox, Ori D.; Johansson, Joel; Kasliwal, Mansi M.; Andrews, Jennifer E.; Bally, John; Bond, Howard E.; Boyer, Martha L.; Gehrz, R. D.; Helou, George; Hsiao, E. Y.; Masci, Frank J.; Parthasarathy, M.; Smith, Nathan; Tinyanont, Samaporn; Van Dyk , Schuyler D.
Supernovae Type Iax (SNe Iax) are less energetic and less luminous than
typical thermonuclear explosions. A suggested explanation for the observed
characteristics of this subclass is a binary progenitor system consisting of a
CO white dwarf primary accreting from a helium star companion. A
single-degenerate explosion channel might be expected to result in a dense
circumstellar medium (CSM), although no evidence for such a CSM has yet been
observed for this subclass. Here we present recent Spitzer observations of the
SN Iax 2014dt obtained by the SPIRITS program nearly one year post-explosion
that reveal a strong mid-IR excess over the expected fluxes of more normal SNe
Ia. This excess...
MCViNE - An object oriented Monte Carlo neutron ray tracing simulation package - Lin, Jiao Y. Y.; Smith, Hillary L.; Granroth, Garrett E.; Abernathy, Douglas L.; Lumsden, Mark D.; Winn, Barry; Aczel, Adam A.; Aivazis, Michael; Fultz, Brent
MCViNE (Monte-Carlo VIrtual Neutron Experiment) is a versatile Monte Carlo (MC) neutron ray-tracing program that provides researchers with tools for performing computer modeling and simulations that mirror real neutron scattering experiments. By adopting modern software engineering practices such as using composite and visitor design patterns for representing and accessing neutron scatterers, and using recursive algorithms for multiple scattering, MCViNE is flexible enough to handle sophisticated neutron scattering problems including, for example, neutron detection by complex detector systems, and single and multiple scattering events in a variety of samples and sample environments. In addition, MCViNE can take advantage of simulation components...
A population-based temporal logic gate for timing and recording chemical events - Hsiao, Victoria; Hori, Yutaka; Rothemund, Paul W. K.; Murray, Richard M.
Single-cell bacterial sensors have numerous applications in human health monitoring, environmental chemical detection, and materials biosynthesis. Such bacterial devices need not only the capability to differentiate between combinations of inputs, but also the ability to process signal timing and duration. In this work, we present a two-input temporal logic gate that can sense and record the order of the inputs, the timing between inputs, and the duration of input pulses. The temporal logic gate design relies on unidirectional DNA recombination with bacteriophage integrases to detect and encode sequences of input events. When implemented in a chromosomally-modified E. coli strain, we...
Windowed Green Function method for layered-media scattering - Bruno, Oscar P.; Lyon, Mark; Pérez-Arancibia, Carlos; Turc, Catalin
This paper introduces a new Windowed Green Function (WGF) method for the numerical integral-equation solution of problems of electromagnetic scattering by obstacles in presence of dielectric or conducting half-planes. The WGF method, which is based on use of smooth windowing functions and integral kernels that can be expressed directly in terms of the free-space Green function, does not require evaluation of expensive Sommerfeld integrals. The proposed approach is fast, accurate, flexible and easy to implement. In particular, straightforward modifications of existing (accelerated or unaccelerated) solvers suffice to incorporate the WGF capability. The mathematical basis of the method is simple: the...
A Research Program on Solid Propellant Physical Behavior - Tshoegl, N. W.; Landel, R. F.; Kausch, H.; Lim, C. K.; Mancke, R. G.; Fesko, D. G.; Yagii, K.
This report presents the results obtained during the past year in a research program on Solid Propellant Physical Behavior carried out at the California Institute of Technology with the support of the U.S. Air Force
Rocket Propulsion Laboratory, Lt. Scott Beckwith, Project Engineer, under Contract No. F-4611-67-C-0057. The object of the research program is to contribute to our under standing of the physical behavior of solid propellants
through a comprehensive study of filled elastomeric systems.
Analytical Studies of Steady and Non-Steady Motions of a Bubbly Liquid - Symington, William A.
A consistent set of continuum-like equations which describe,
under certain limitations, the flow of bubbly gas-liquid mixtures is applied in the solution of a few problems that bear on technological issues of nuclear reactor safety. The solutions of these problems illustrate the significance of the ratio between the viscous relaxation time of the bubbles and the characteristic time of the flow,
in scaling experimental results.
The choked flow of a bubbly mixture through a contraction in
a one-dimensional duct is treated. It is found that in many cases the ratio of the contraction residence time to the viscous relaxation time is small, indicating the...