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Caltech Authors (134.378 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 3.739

  1. Three-dimensional Boltzmann-Hydro code for core-collapse in massive stars II. The Implementation of moving-mesh for neutron star kicks

    Nagakura, Hiroki; Iwakami, Wakana; Furusawa, Shun; Sumiyoshi, Kohsuke; Yamada, Shoichi; Matsufuru, Hideo; Imakura, Akira
    We present a newly developed moving-mesh technique for the multi-dimensional Boltzmann-Hydro code for the simulation of core-collapse supernovae (CCSNe). What makes this technique different from others is the fact that it treats not only hydrodynamics but also neutrino transfer in the language of the 3+1 formalism of general relativity (GR), making use of the shift vector to specify the time evolution of the coordinate system. This means that the transport part of our code is essentially general relativistic although in this paper it is applied only to the moving curvilinear coordinates in the flat Minknowski spacetime, since the gravity part is...

  2. Spectral Line De-confusion in an Intensity Mapping Survey

    Cheng, Yun-Ting; Chang, Tzu-Ching; Bock, James J.; Bradford, C. Matt; Cooray, Asantha
    Spectral line intensity mapping has been proposed as a promising tool to efficiently probe the cosmic reionization and the large-scale structure. Without detecting individual sources, line intensity mapping makes use of all available photons and measures the integrated light in the source confusion limit, to efficiently map the three-dimensional matter distribution on large scales as traced by a given emission line. One particular challenge is the separation of desired signals from astrophysical continuum foregrounds and line interlopers. Here we present a technique to extract large-scale structure information traced by emission lines from different redshifts, embedded in a three-dimensional intensity mapping data...

  3. Spectrum-splitting approach for Fermi-operator expansion in all-electron Kohn-Sham DFT calculations

    Motamarri, Phani; Gavini, Vikram; Bhattacharya, Kaushik; Ortiz, Michael
    We present a spectrum-splitting approach to conduct all-electron Kohn-Sham density functional theory (DFT) calculations by employing Fermi-operator expansion of the Kohn-Sham Hamiltonian. The proposed approach splits the subspace containing the occupied eigenspace into a core-subspace, spanned by the core eigenfunctions, and its complement, the valence-subspace, and thereby enables an efficient computation of the Fermi-operator expansion by reducing the expansion to the valence-subspace projected Kohn-Sham Hamiltonian. The key ideas used in our approach are: (i) employ Chebyshev filtering to compute a subspace containing the occupied states followed by a localization procedure to generate non-orthogonal localized functions spanning the Chebyshev-filtered subspace; (ii)...

  4. A threshold-force model for adhesion and mode I fracture

    Hulikal, Srivatsan; Bhattacharya, Kaushik; Lapusta, Nadia
    We study the relation between a threshold-force based model at the microscopic scale and mode I fracture at the macroscopic scale in a system of discrete interacting springs. Specifically, we idealize the contact between two surfaces as that between a rigid surface and a collection of springs with long-range interaction and a constant tensile threshold force. We show that a particular scaling similar to that of crack-tip stress in Linear Elastic Fracture Mechanics leads to a macroscopic limit behavior. The model also reproduces the scaling behaviors of the JKR model of adhesive contact. We determine how the threshold force depends...

  5. The Rate of Binary Black Hole Mergers Inferred from Advanced LIGO Observations Surrounding 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.; Bork, R.; Brooks, A. F.; Cahillane, C.; Callister, T.; Cepeda, C. B.; Chakraborty, R.; Chalermsongsak, T.; Chen, Y.; Couvares, P.; Coyne, D. C.; Dergachev, V.; Drever, R. W. P.; Ehrens, P.; Engels, W.; 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.; Thorne, K. S.; Torrie, C. I.; Vajente, G.; Vallisneri, M.; Vass, S.; Wallace, L.; Weinstein, A. J.; Williams, R. D.; Wipf, C. C.; Yamamoto, H.; Zhang, L.; Zucker, M. E.; Zweizig, J.
    A transient gravitational-wave signal, GW150914, was identified in the twin Advanced LIGO detectors on September 14, 2015 at 09:50:45 UTC. To assess the implications of this discovery, the detectors remained in operation with unchanged configurations over a period of 39 d around the time of the signal. At the detection statistic threshold corresponding to that observed for GW150914, our search of the 16 days of simultaneous two-detector observational data is estimated to have a false alarm rate (FAR) of < 4.9 × 10^(−6) yr^(−1), yielding a p-value for GW150914 of < 2 × 10^(−7). Parameter estimation followup on this trigger...

  6. A Constant Ratio between Black Hole Accretion and Star Formation in IR-bright AGNs

    Dai, Y. Sophia; Wilkes, Belinda J.; Bergeron, Jacqueline; Omont, Alain; Kuraszkiewicz, Joanna; Atanas, Adam; Teplitz, Harry I.
    We study the relationship between the X-ray luminosity and star formation rate (SFR) in a sample of farinfrared(FIR)-detected active galactic nuclei (AGNs). This IR-bright AGN sample consists of 828 objects in 0.2< z < 2.5, and spans four orders of magnitude in L_X = 10^(42∼46)erg s^(−1). We calculated the SFR from the AGN-removed IR luminosity based on spectral energy distribution (SED) fitting. We observe a strong correlation between L_(AGN) and SFR, after removing the redshift effect. We notice that binning the sample by SFR instead of L_(AGN) results in a stronger correlation, consistent with the shorter timescale and larger amplitude...

  7. The Influence of Neutrinos on r-Process Nucleosynthesis in the Ejecta of Black Hole-Neutron Star Mergers

    Roberts, Luke F.; Lippuner, Jonas; Duez, Matthew D.; Faber, Joshua A.; Foucart, Francois; Lombardi, James C., Jr.; Ning, Sandra; Ott, Christian D.; Ponce, Marcelo
    During the merger of a black hole and a neutron star, baryonic mass can become unbound from the system. Because the ejected material is extremely neutron-rich, the r-process rapidly synthesizes heavy nuclides as the material expands and cools. In this work, we map general relativistic models of black hole{neutron star (BHNS) mergers into a Newtonian smoothed particle hydrodynamics (SPH) code and follow the evolution of the thermodynamics and morphology of the ejecta until the out ows become homologous. We investigate how the subsequent evolution depends on our mapping procedure and find that the results are robust. Using thermodynamic histories from the SPH...

  8. A neutron star progenitor for FRBs? Insights from polarisation measurements

    Ravi, Vikram; Lasky, Paul D.
    Fast Radio Bursts (FRBs) are intense, millisecond-duration broadband radio tran- sients, the emission mechanisms of which are not understood. Masui et al. recently presented Green Bank Telescope observations of FRB 110523, which displayed tem- poral variation of the linear polarisation position angle (PA). This effect is commonly seen in radio pulsars and is attributed to a changing projected magnetic field orien- tation in the emission region as the star rotates. If a neutron star is the progenitor of this FRB, and the emission mechanism is pulsar-like, we show that the progenitor is either rapidly rotating, or the emission originates from a region of complex mag- netic field geometry....

  9. Tomographic reflection modelling of quasi-periodic oscillations in the black hole binary H 1743-322

    Ingram, Adam; van der Klis, Michiel; Middleton, Matthew; Altamirano, Diego; Uttley, Phil
    Accreting stellar mass black holes (BHs) routinely exhibit Type-C quasi-periodic oscillations (QPOs). These are often interpreted as Lense-Thirring precession of the inner accretion flow, a relativistic effect whereby the spin of the BH distorts the surrounding space-time, inducing nodal precession. The best evidence for the precession model is the recent discovery, using a long joint XMM-Newton and NuSTAR observation of H 1743-322, that the centroid energy of the iron fluorescence line changes systematically with QPO phase. This was interpreted as the inner flow illuminating different azimuths of the accretion disc as it precesses, giving rise to a blue/red shifted iron line when the approaching/receding disc material is illuminated. Here,...

  10. Multi-wavelength observations of IGR J17544-2619 from quiescence to outburst

    Bozzo, E.; Bhalerao, V.; Pradhan, P.; Tomsick, J.; Romano, P.; Ferrigno, C.; Chaty, S.; Oskinova, L.; Manousakis, A.; Walter, R.; Falanga, M.; Campana, S.; Stella, L.; Ramolla, M.; Chini, R.
    In this paper we report on a long multi-wavelength observational campaign of the supergiant fast X-ray transient prototype IGR J17544-2619. A 150 ks-long observation was carried out simultaneously with XMM-Newton and NuSTAR, catching the source in an initial faint X-ray state and then undergoing a bright X-ray outburst lasting about 7 ks. We studied the spectral variability during outburst and quiescence by using a thermal and bulk Comptonization model that is typically adopted to describe the X-ray spectral energy distribution of young pulsars in high mass X-ray binaries. Although the statistics of the collected X-ray data were relatively high we could neither confirm the presence of a cyclotron line...

  11. Cold Matter Assembled Atom-by-Atom

    Endres, Manuel; Bernien, Hannes; Keesling, Alexander; Levine, Harry; Anschuetz, Eric R.; Krajenbrink, Alexandre; Senko, Crystal; Vuletic, Vladan; Greiner, Markus; Lukin, Mikhail D.
    The realization of large-scale fully controllable quantum systems is an exciting frontier in modern physical science. We use atom-by-atom assembly to implement a novel platform for the deterministic preparation of regular arrays of individually controlled cold atoms. In our approach, a measurement and feedback procedure eliminates the entropy associated with probabilistic trap occupation and results in defect-free arrays of over 50 atoms in less than 400 ms. The technique is based on fast, real-time control of 100 optical tweezers, which we use to arrange atoms in desired geometric patterns and to maintain these configurations by replacing lost atoms with surplus...

  12. A First Targeted Search for Gravitational-Wave Bursts from Core-Collapse Supernovae in Data of First-Generation Laser Interferometer Detectors

    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.; 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.; Kalmus, P.; 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.; 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.; Santamaría, L.; 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. E.; Williams, R. D.; Wipf, C. C.; Yamamoto, H.; Zhang, L.; Zucker, M. E.; Zweizig, J.; Chen, Y.; Engels, W.; Ott, C. D.; Thorne, K. S.
    We present results from a search for gravitational-wave bursts coincident with two core-collapse supernovae observed optically in 2007 and 2011. We employ data from the Laser Interferometer Gravitational-wave Observatory (LIGO), the Virgo gravitational-wave observatory, and the GEO600 gravitational-wave observatory. The targeted core-collapse supernovae were selected on the basis of (1) proximity (within approximately 15Mpc), (2) tightness of observational constraints on the time of core collapse that defines the gravitational-wave search window, and (3) coincident operation of at least two interferometers at the time of core collapse. We find no plausible gravitational-wave candidates. We present the probability of detecting signals from both astrophysically well-motivated and more...

  13. Laser Interferometers as Dark Matter Detectors

    Hall, Evan D.; Callister, Thomas; Frolov, Valery V.; Müller, Holger; Pospelov, Maxim; Adhikari, Rana X.
    While global cosmological and local galactic abundance of dark matter is well established, its identity, physical size and composition remain a mystery. In this paper, we analyze an important question of dark matter detectability through its gravitational interaction, using current and next generation gravitational-wave observatories to look for macroscopic (kilogram-scale or larger) objects. Keeping the size of the dark matter objects to be smaller than the physical dimensions of the detectors, and keeping their mass as free parameters, we derive the expected event rates. For favorable choice of mass, we find that dark matter interactions could be detected in space-based detectors such as LISA at a...

  14. How fast do stabilizer Hamiltonians thermalize?

    Temme, Kristan; Kastoryano, Michael
    We present rigorous bounds on the thermalization time of the family of quantum mechanical spin systems known as stabilizer Hamiltonians. The thermalizing dynamics are modeled by a Davies master equation that arises from a weak local coupling of the system to a large thermal bath. Two temperature regimes are considered. First we clarify how in the low temperature regime, the thermalization time is governed by a generalization of the energy barrier between orthogonal ground states. When no energy barrier is present the Hamiltonian thermalizes in a time that is at most quadratic in the system size. Secondly, we show that above a universal critical temperature, every...

  15. Resonant Thermoelectric Nanophotonics

    Mauser, Kelly W.; Mitrovic, Slobodan; Kim, Seyoon; Fleischman, Dagny; Atwater, Harry A.
    Photodetectors are typically based on photocurrent generation from electron-hole pairs in semiconductor structures and on bolometry for wavelengths that are below bandgap absorption. In both cases, resonant plasmonic and nanophotonic structures have been successfully used to enhance performance. In this work, we demonstrate subwavelength thermoelectric nanostructures designed for resonant spectrally selective absorption, which creates large enough localized temperature gradients to generate easily measureable thermoelectric voltages. We show that such structures are tunable and are capable of highly wavelength specific detection, with an input power responsivity of up to 119 V/W (referenced to incident illumination), and response times of nearly 3...

  16. High energy properties of the flat spectrum radio quasar 4C 50.11

    Zhou, Jianeng; Jithesh, V.; Liang, Chen; Wang, Zhongxiang
    We investigate the gamma-ray and X-ray properties of the flat spectrum radio quasar (FSRQ) \4c50 at redshift z= 1.517. The Fermi Large Area Telescope (LAT) data indicate that this source was in an active state since 2013 July. During the active period, the gamma-ray flux increased by more than a factor of three and two distinct flares were detected with the variability timescale as short as several hours. The gamma-ray spectra can be well fitted by a log-parabola. From the fitting, we find a correlation between the peak energy and spectral curvature for the gamma-ray spectra, which is the first time seen in gamma-ray emission from a blazar....

  17. A FIR-Survey of TNOs and Related Bodies

    Bauer, J. M.; Goldsmith, P. F.; Bradford, C. M.; Lovell, A. J.
    The small solar-system bodies that reside between 30 and 50 AU are often referred to as the Trans Neptunian Objects, or TNOs. A far-infrared (FIR) mission with survey capabilities, like the prospective Cryogenic Aperture Large Infrared Space Telescope Observatory (CALISTO; Goldsmith et al. 2008), offers the potential for the first time of really probing the population of TNOs, and related populations, down to moderates sizes, and out to distances exceeding 100 AU from the Sun.

  18. Wide-field Fourier ptychographic microscopy using laser illumination source

    Chung, Jaebum; Lu, Hangwen; Ou, Xiaoze; Zhou, Haojiang; Yang, Changhuei
    Fourier ptychographic (FP) microscope is a coherent imaging method that can synthesize an image with a higher bandwidth using multiple low-bandwidth images captured at different spatial frequency regions. The method's demand for multiple images drives the need for a brighter illumination scheme and a high-frame-rate camera for a faster acquisition. We report the use of a guided laser beam as an illumination source for an FP microscope. It uses a mirror array and a 2-dimensional scanning Galvo mirror system to provide a sample with plane-wave illuminations at diverse incidence angles. The use of a laser presents speckles in the image...

  19. Predicting Whole Forest Structure, Primary Productivity, and Biomass Density From Maximum Tree Size and Resource Limitations

    Kempes, Christopher P.; Choi, Sungho; Dooris, William; West, Geoffrey B.
    In the face of uncertain biological response to climate change and the many critiques concerning model complexity it is increasingly important to develop predictive mechanistic frameworks that capture the dominant features of ecological communities and their dependencies on environmental factors. This is particularly important for critical global processes such as biomass changes, carbon export, and biogenic climate feedback. Past efforts have successfully understood a broad spectrum of plant and community traits across a range of biological diversity and body size, including tree size distributions and maximum tree height, from mechanical, hydrodynamic, and resource constraints. Recently it was shown that global...

  20. Campaign 9 of the K2 Mission: Observational Parameters, Scientific Drivers, and Community Involvement for a Simultaneous Space- and Ground-based Microlensing Survey

    Henderson, Calen B.; Calchi Novati, S.; Akeson, R.; Beichman, C. A.; Ciardi, D.; Gelino, C.
    K2's Campaign 9 (K2C9) will conduct a ∼3.7 deg^2 survey toward the Galactic bulge from 7/April through 1/July of 2016 that will leverage the spatial separation between K2 and the Earth to facilitate measurement of the microlens parallax πE for ≳127 microlensing events. These will include several that are planetary in nature as well as many short-timescale microlensing events, which are potentially indicative of free-floating planets (FFPs). These satellite parallax measurements will in turn allow for the direct measurement of the masses of and distances to the lensing systems. In this white paper we provide an overview of the K2C9...

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