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Caltech Authors (95,836 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 3,992

1. An OSSE Search for the Binary Radio Pulsar 1259-63 - Ray, P. S.; Grove, J. E.; Kurfess, J.D.; Prince, Thomas A.; Ulmer, M. P.
We have searched data from the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (GRO) for evidence of low‐energy γ‐ray emission from the binary radio pulsar PSR1259−63. This 47 ms pulsar is in a long‐period, highly eccentric orbit around a Be stellar companion and was observed by OSSE approximately 400 days after periastron. The period derivative allowed by the published radio ephemeris (Johnston et al. 1992) suggests that the pulsar might be relatively young, and therefore a γ‐ray source. However, the ephemeris is not sufficiently accurate to allow the traditional epoch‐folding technique over the full OSSE observation....

2. A Science Center for the Advanced Composition Explorer - Garrard, T. L.; Hammond, J. S.
The Advanced Composition Explorer (ACE) mission is supported by an ACE Science Center for the purposes of facilitating collaborative work. It is intended that coordinated use of a centralized science facility by the ACE team will ensure appropriate use of data formatting standards, thus easing access to the data; will improve communications within and to the ACE science working team; and will reduce redundant effort in data processing.

3. Demo Abstract: Distributed Control of a Swarm of Buildings Connected to a Smart Grid - Aksanli, Baris; Akyurek, Alper S.; Behl, Madhur; Clark, Meghan; Donzé, Alexandre; Dutta, Prabal; Lazik, Patrick; Mehdi, Maasoumy; Mangharam, Raul; Nghiem, Truong X.; Raman, Vasumathi; Rowe, Anthony; Sangiovanni-Vincentelli, Alberto; Seshia, Sanjit A.; Rosing, Tajana Simunic; Venkatesh, Jagannathan
Energy-efficient control mechanisms are necessary to manage the ever increasing energy demand. Recently several tools for building energy consumption control have been proposed for small (e.g. homes) and large (e.g. offices) buildings. The mechanism each tool uses is different, e.g. HVAC control and appliance rescheduling, but they share the goal of improving consumption of the buildings with respect to a given cost function. Some examples of cost functions are reduced energy consumption, reduced electricity bill, lower peak power, and increased ancillary service participation. The tools however do not capture the impacts of their control actions on the grid. These actions...

4. VIP: A Framework for Joint Dynamic Forwarding and Caching in Named Data Networks - Yeh, Edmund; Ho, Tracey; Cui, Ying; Burd, Michael; Liu, Ran; Leong, Derek
Emerging information-centric networking architectures seek to optimally utilize both bandwidth and storage for efficient content distribution. This highlights the need for joint design of traffic engineering and caching strategies, in order to optimize network performance in view of both current traffic loads and future traffic demands. We present a systematic framework for joint dynamic interest request forwarding and dynamic cache placement and eviction, within the context of the Named Data Networking (NDN) architecture. The framework employs a virtual control plane which operates on the user demand rate for data objects in the network, and an actual plane which handles Interest...

5. Towards Managed Terabit/s Scientific Data Flows - Barczyk, Artur; Mughal, Azher; Newman , Harvey; Legrand, Iosif; Bredel, Michael; Voicu, Ramiro; Lapadatescu, Vlad; Wildish, Tony
Scientific collaborations on a global scale, such as the LHC experiments at CERN [1], rely today on the presence of high performance, high availability networks. In this paper we review the developments performed over the last several years on high throughput applications, multilayer software-defined network path provisioning, path selection and load balancing methods, and the integration of these methods with the mainstream data transfer and management applications of CMS [2], one of the major LHC experiments. These developments are folded into a compact system capable of moving data among research sites at the 1 Terabit per second scale. Several aspects...

6. Remarks on a Question of Ericksen Concerning Elastostatic Fields of Saint-Venant Type - Knowles, James K.
In an effort to understand better the relationship between approximate theories —such as those for thin rods—and the three-dimensional theory of elasticity, Ericksen [1]–[3] has recently suggested a reconsideration of Saint-Venant’s problem for elastic cylinders with traction-free lateral surfaces. Among the various questions raised in [1]–[3], one concerns the structure and role of the set of all possible elastostatic fields in an infinitely long cylinder in the absence of lateral loading and body force, but in the presence of a restriction on the size of a suitable cross-sectional norm of the associated strain tensor field.

7. Modeling the Modulatory Effect of Attention on Human Spatial Vision - Itti, Laurent; Braun, Jochen; Koch, Christof
We present new simulation results, in which a computational model of interacting visual neurons simultaneously predicts the modulation of spatial vision thresholds by focal visual attention, for five dual-task human psychophysics experiments. This new study complements our previous findings that attention activates a winner-take-all competition among early visual neurons within one cortical hypercolumn. This "intensified competition" hypothesis assumed that attention equally affects all neurons, and yielded two single-unit predictions: an increase in gain and a sharpening of tuning with attention. While both effects have been separately observed in electrophysiology, no single-unit study has yet shown them simultaneously. Hence, we here explore whether...

8. Research on Mechanisms of Exciting Pressure Oscillations in Ramjet Engines - Culick, F. E. C.; Marble, Frank E.; Zukoski, E. E.
An analytical and experimental study is being made of the role of combustion in large vortical structures in the mechanism of unsteady and unstable burning in air-breathing engines. A large body of experimental evidence supports the contention that these periodic fluctuations are themselves generated by the nonsteady flow over the flame holders and other surfaces. The mechanism itself is relatively independent of the acoustic configuration of the powerplant and its installation and hence constitutes the fundamental element of the combustion instability process. Whether or not the mechanism is excited does, however, depend upon the detailed acoustic properties of the combustion chamber and...

9. Chemical Reactions in Turbulent Mixing Flows - Liepmann, H. W.; Broadwell, J. E.; Dimotakis, P. E.
This is a continuing effort in both gas phase and liquid phase mixing, chemical reactions and combustion, in moderate to high Reynolds number turbulent free shear flows. This is primarily an experimental investigation closely supported by theoretical and modeling efforts, as well as specific diagnostics developments, as dictated by specific needs of the experimental program.

10. Structure and Mixing in Turbulent Shear Flows - Roshko, Anatol
The broad problem being addressed in our research is to identify and describe the primary vortical ("coherent", "organized") large structures in various turbulent shear flows; to determine how they contribute to the mixing processes; and to make use of them in modelling and in possibly controlling or modifying those flows. Accumulating experimental evidence suggests that these primary vortical structures are different in different shear flows. Conclusions which follow from these views are that (i) there cannot be a universal turbulence model for these different flows; and (ii) existence of such structures implies the possibility of their manipulation or control and thus modification of...

11. Unsteady wind loads for TMT: Replacing parametric models with CFD - MacMartin, Douglas G.; Vogiatzis, Konstantinos
Unsteady wind loads due to turbulence inside the telescope enclosure result in image jitter and higher-order image degradation due to M1 segment motion. Advances in computational fluid dynamics (CFD) allow unsteady simulations of the flow around realistic telescope geometry, in order to compute the unsteady forces due to wind turbulence. These simulations can then be used to understand the characteristics of the wind loads. Previous estimates used a parametric model based on a number of assumptions about the wind characteristics, such as a von Karman spectrum and frozen-flow turbulence across M1, and relied on CFD only to estimate parameters such...

12. NuSTAR observatory science operations: on-orbit acclimation - Foster, Karl; Harrison, Fiona A.; Dodd, Suzanne R.; Stern, Daniel K.; Miyasaka, Hiromasa; Madsen, Kristin K.; Grefenstette, Brian W.; Markwardt, Craig B.; Craig, William W.; Marshall, Francis E.
The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing high energy (3-79 keV) X-ray observatory. The NuSTAR project is led by Caltech, which hosts the Science Operations Center (SOC), with mission operations managed by UCB Space Sciences Laboratory. We present an overview of NuSTAR science operations and describe the on-orbit performance of the observatory. The SOC is enhancing science operations to serve the community with a guest observing program beginning in 2015. We present some of the challenges and approaches taken by the SOC to operating a full service space observatory that maximizes the scientific return from the mission.

13. Microdosimetry and physiological effects of millimeter wave irradiation in isolated neural ganglion preparation - Romanenko, Sergii; Siegel, Peter H.; Pikov, Victor
Possible effects of millimeter waves (MMWs) on biological objects becomes an increasingly important issue due to development of technologies for telecommunication, telemedicine and security/military applications operating at this extremely high radiofrequency band. Specifically, the safety limits of MMW irradiation of neuronal tissue need to be evaluated. In this study, we evaluated the thermal and physiological effects of MMWs on the neural ganglia isolated from the leech. The initial results indicate that low-intensity MMWs can partially suppress the neuronal activity at relatively low levels of applied MMW power density, with associated sub-1°C heating of the ganglion. Further studies are underway to...

14. Microscopic processes on a fault plane and their implications for earthquake dynamics - Kanamori, Hiroo; Mori, Jim
Seismic radiation exhibits complex wave forms. The complexity can be due to both static and dynamic mechanisms. Static mechanisms responsible for complexity are roughness and heterogeneities of rock properties on a fault plane. Many dynamic mechanisms are possible, but thermal processes caused by frictional heating are most likely to cause complex and chaotic behavior of seismic rupture through nonlinear feedback mechanisms. Similarity of the beginning of small and large earthquakes suggests that a cascade process that can be simulated by percolation models provides a realistic model of complex earthquake rupture. A percolation process results in a relation similar to the magnitude-frequency relationship for earthquakes. As the state of the...

15. Detonation Initiation via Imploding Shock Waves - Jackson, S. I.; Shepherd, J. E.
An imploding annular shock wave driven by a jet of air was used to initiate detonations inside a 76 mm diameter tube. The tube was filled with a test gas composed of either stoichiometric ethylene-oxygen or propane-oxygen diluted with nitrogen. The strength of the imploding shock wave and the sensitivity of the test gas were varied in an effort to find the minimum shock strength required for detonation of each test mixture. The results show that the minimum required shock strength increases with mixture sensitivity and suggest that impractically large shock driver pressures are required to initiate detonations in ethylene-air or propane-air mixtures when using this technique.

16. Earthquake Prediction: An Overview - Kanamori, Hiroo
This chapter focuses on prediction of earthquakes. Because earthquakes occur suddenly, often with devastating consequences, earthquake prediction is a matter of great interest among the public and emergency service officials. The term “earthquake prediction” is often used to mean two different things. In the common usage, especially among the public, “earthquake prediction” means a highly reliable, publicly announced, short-term (within hours to weeks) prediction that will prompt some emergency measures (e.g., alert, evacuation, etc.). Exactly how reliable this type of prediction should be depends on the social and economic situations of the region involved. The issue is whether the quality...

17. The Nature of Seismicity Patterns Before Large Earthquakes - Kanamori, Hiroo
Various seismicity patterns before major earthquakes have been reported in the literature. They include foreshocks (broad sense), preseismic quiescence, precursory swarms, and doughnut patterns. Although many earthquakes are preceded by all, or some, of these patterns, their detail differ significantly from event to event. In order to examine the details of seismicity patterns on as uniform a basis as possible, we made space-time plots of seismicity for many large earthquakes by using the NOAA and JMA catalogs. Among various seismicity patterns, preseismic quiescence appears most common, the case for the 1978 Oaxaca earthquake being the most prominent. Although the nature of...

18. The Origin of the Tsunami Excited by the Earthquake – Faulting or Slumping - Ma, Kuo-Fong; Satake, Kenji; Kanamori, Hiroo
The first arrival of the tsunami recorded at Monterey, California, was about 10 min after the origin time of the earthquake. Using an elastic half space, we computed vertical ground displacements for many different fault models for the Loma Prieta earthquake and used them as the initial condition for computation of the tsunami in Monterey Bay. The synthetic tsunami computed for the uniform dislocation model determined from seismic data can explain the arrival time, polarity, and amplitude of the beginning of the tsunami. However, the period of the synthetic tsunami is too long compared with the observed. We tested other fault models with more localized slip distribution. None of the models could...

19. Broadband Study of the Source Characteristics of the Earthquake - Kanamori, Hiroo; Satake, Kenji
We have determined the source characteristics of the 1989 Loma Prieta earthquake, using teleseismic data. The solution from body waves gives a mechanism with a strike of 128°, a dip of 70° a rake of 138°, and a seismic moment of 3x10^(26)dyne-cm (M_w=6.9). This solution is similar to those obtained from long-period Rayleigh and Love waves, PnJ waves, and first-motion data. The body-wave solution suggests a depth of about 15 km. The effective duration of the source is 6 s, suggesting lengths of 30 and 15 km for bilateral and unilateral faulting, respectively. Considering the extent of the aftershock zones, we estimate a total rupture length of 35 km. The strike-slip...

20. An asperity model of large earthquake sequences - Lay, Thorne; Kanamori, Hiroo
The variation in maximum rupture extent of large shallow earthquakes in circum-Pacific subduction zones is interpreted in the context of the asperity model of stress distribution on the fault plane. Comparison of the historic record of large earthquakes in different zones indicates that four fundamental categories of behavior are observed. These are: (1) the Chile-type regular occurrence of great ruptures spanning more than 500 km; (2) the Aleutians-type variation in rupture extent with occasional ruptures up to 500 km long, and temporal clustering of large events; (3) the Kurile-type repeated failure over a limited zone of 100–300 km length in...

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