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Caltech Authors (163.728 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 1.213

  1. On the Nature of the High-Energy Rollover in 1H 0419-577

    Turner, T. J.; Reeves, J. N.; Braito, V.; Costa, M.
    A NuSTAR/Swift observation of the luminous Seyfert 1 galaxy 1H 0419-577 taken during 2015 reveals one of the most extreme high energy cut-offs observed to date from an AGN - an origin due to thermal Comptonization would imply a remarkably low coronal temperature $kT \sim 15$ keV. The low energy peak of the spectrum in the hard X-ray NuSTAR band, which peaks before the expected onset of a Compton hump, rules out strong reflection as the origin of the hard excess in this AGN. We show the origin of the high energy rollover is likely due to a combination of both thermal Comptonization and an intrinsically steeper continuum,...

  2. Probing many-body localization in a disordered quantum magnet

    Silevitch, D. M.; Aeppli, G.; Rosenbaum, T. F.
    Excitations in disordered systems are typically categorized as localized or delocalized, depending on whether they entail disturbances extending throughout the system or are confined to small, generally nanometer scale, subsystems. Such categorization is impossible to achieve using traditional spectroscopy where the response to a weak oscillating (ac) electromagnetic probe is measured as a function of frequency. However, the localized excitations can be separated from each other as well as the delocalized continuum by measuring a spectral "hole" in the ordinary response while a large amplitude pump is imposed at a fixed frequency. Localized excitations will result in a very sharp...

  3. Observing the Cell in Its Native State: Imaging Subcellular Dynamics in Multicellular Organisms

    Liu, Tsung-Li; Ruan, Yuan; Yashiro, Hanako; Meyerowitz, Elliot M.
    True physiological imaging of subcellular dynamics requires studying cells within their parent organisms, where all the environmental cues that drive gene expression, and hence the phenotypes we actually observe, are present. A complete understanding also requires volumetric imaging of the cell and its surroundings at high spatiotemporal resolution without inducing undue stress on either. We combined lattice light sheet microscopy with two-channel adaptive optics to achieve, across large multicellular volumes, noninvasive aberration-free imaging of subcellular processes, including endocytosis, organelle remodeling during mitosis, and the migration of axons, immune cells, and metastatic cancer cells in vivo. The technology reveals the phenotypic...

  4. Fermion condensation and super pivotal categories

    Aasen, David; Lake, Ethan; Walker, Kevin
    We study fermionic topological phases using the technique of fermion condensation. We give a prescription for performing fermion condensation in bosonic topological phases which contain a fermion. Our approach to fermion condensation can roughly be understood as coupling the parent bosonic topological phase to a phase of physical fermions, and condensing pairs of physical and emergent fermions. There are two distinct types of objects in fermionic theories, which we call "m-type" and "q-type" particles. The endomorphism algebras of q-type particles are complex Clifford algebras, and they have no analogues in bosonic theories. We construct a fermionic generalization of the tube...

  5. The outflow structure of GW170817 from late time broadband observations

    Troja, E.; Piro, L.; Ryan, G.; van Eerten, H.; Ricci, R.; Wieringa, M.; Lotti, S.; Sakamoto, T.; Cenko, S. B.
    We present our broadband study of GW170817 from radio to hard X-rays, including Chandra and NuStar observations, and a multi-messenger analysis including LIGO constraints. The data are compared with predictions from a wide range of models, providing the first detailed comparison between non-trivial cocoon and jet models. Homogeneous and power-law shaped jets, as well as simple cocoon models are ruled out by the data, while both a Gaussian shaped jet and a cocoon with energy injection are found to be consistent with the present data. We propose that these models can be unambiguously discriminated by future observations measuring the post-peak behaviour, with temporal slope -1.2 for the cocoon and...

  6. Non-Gaussian Enhancements of Galactic Halo Correlations in Quasi-Single Field Inflation

    An, Haipeng; McAneny, Michael; Ridgway, Alexander K.; Wise, Mark B.
    We consider a quasi-single field inflation model in which the inflaton interacts with a massive scalar field called the isocurvaton. Due to the breaking of time translational invariance by the inflaton background, these interactions induce kinetic mixing between the inflaton and isocurvaton, which is parameterized by a constant μ. We derive analytic formulae for the curvature perturbation two-, three-, four-, five-, and six-point functions explicitly in terms of the external wave-vectors in the limit where μ and the mass of the isocurvaton m are both much smaller than H. In previous work, it has been noted that when m/H and...

  7. Non-Gaussian Enhancements of Galactic Halo Correlations in Quasi-Single Field Inflation

    An, Haipeng; McAneny, Michael; Ridgway, Alexander K.; Wise, Mark B.
    We consider a quasi-single field inflation model in which the inflaton interacts with a massive scalar field called the isocurvaton. Due to the breaking of time translational invariance by the inflaton background, these interactions induce kinetic mixing between the inflaton and isocurvaton, which is parameterized by a constant μ. We derive analytic formulae for the curvature perturbation two-, three-, four-, five-, and six-point functions explicitly in terms of the external wave-vectors in the limit where μ and the mass of the isocurvaton m are both much smaller than H. In previous work, it has been noted that when m/H and...

  8. Heterogeneous Responses of Hematopoietic Stem Cells to Inflammatory Stimuli are Altered with Age

    Mann, Mati; Mehta, Arnav; de Boer, Carl; Kowalczyk, Monika S.; Lee, Kevin; Rogel, Noga; Knecht, Abigail R.; Farouq, Daneyal; Regev, Aviv; Baltimore, David
    Long-term hematopoietic stem cells (LT-HSCs) maintain hematopoietic output throughout an animal's lifespan. With age, however, they produce a myeloid-biased output that may lead to poor immune responses to infectious challenge and the development of myeloid leukemias. Here, we show that young and aged LT-HSCs respond differently to inflammatory stress, such that aged LT-HSCs produce a cell-intrinsic, myeloid-biased expression program. Using single-cell RNA-seq, we identify a myeloid-biased subset within the LT-HSC population (mLT-HSCs) that is much more common amongst aged LT-HSCs and is uniquely primed to respond to acute inflammatory challenge. We predict several transcription factors to regulate differentially expressed genes...

  9. Heterogeneous Responses of Hematopoietic Stem Cells to Inflammatory Stimuli are Altered with Age

    Mann, Mati; Mehta, Arnav; de Boer, Carl; Kowalczyk, Monika S.; Lee, Kevin; Rogel, Noga; Knecht, Abigail R.; Farouq, Daneyal; Regev, Aviv; Baltimore, David
    Long-term hematopoietic stem cells (LT-HSCs) maintain hematopoietic output throughout an animal's lifespan. With age, however, they produce a myeloid-biased output that may lead to poor immune responses to infectious challenge and the development of myeloid leukemias. Here, we show that young and aged LT-HSCs respond differently to inflammatory stress, such that aged LT-HSCs produce a cell-intrinsic, myeloid-biased expression program. Using single-cell RNA-seq, we identify a myeloid-biased subset within the LT-HSC population (mLT-HSCs) that is much more common amongst aged LT-HSCs and is uniquely primed to respond to acute inflammatory challenge. We predict several transcription factors to regulate differentially expressed genes...

  10. Heterogeneous Responses of Hematopoietic Stem Cells to Inflammatory Stimuli are Altered with Age

    Mann, Mati; Mehta, Arnav; de Boer, Carl; Kowalczyk, Monika S.; Lee, Kevin; Rogel, Noga; Knecht, Abigail R.; Farouq, Daneyal; Regev, Aviv; Baltimore, David
    Long-term hematopoietic stem cells (LT-HSCs) maintain hematopoietic output throughout an animal's lifespan. With age, however, they produce a myeloid-biased output that may lead to poor immune responses to infectious challenge and the development of myeloid leukemias. Here, we show that young and aged LT-HSCs respond differently to inflammatory stress, such that aged LT-HSCs produce a cell-intrinsic, myeloid-biased expression program. Using single-cell RNA-seq, we identify a myeloid-biased subset within the LT-HSC population (mLT-HSCs) that is much more common amongst aged LT-HSCs and is uniquely primed to respond to acute inflammatory challenge. We predict several transcription factors to regulate differentially expressed genes...

  11. Phase Coherent Link of an Atomic Clock to a Self-Referenced Microresonator Frequency Comb

    Del’Haye, Pascal; Coillet, Aurélien; Fortier, Tara; Beha, Katja; Cole, Daniel C.; Yang, Ki Youl; Lee, Hansuek; Vahala, Kerry J.; Papp, Scott B.; Diddams, Scott A.
    The counting and control of optical cycles of light has become common with modelocked laser frequency combs. But even with advances in laser technology, modelocked laser combs remain bulk-component devices that are hand-assembled. In contrast, a frequency comb based on the Kerr-nonlinearity in a dielectric microresonator will enable frequency comb functionality in a micro-fabricated and chip-integrated package suitable for use in a wide-range of environments. Such an advance will significantly impact fields ranging from spectroscopy and trace gas sensing, to astronomy, communications, atomic time keeping and photonic data processing. Yet in spite of the remarkable progress shown over the past...

  12. Bridging ultra-high-Q devices and photonic circuits

    Yang, Ki Youl; Oh, Dong Yoon; Lee, Seung Hoon; Yang, Qi-Fan; Yi, Xu; Vahala, Kerry
    Optical microcavities are essential in numerous technologies and scientific disciplines. However, their application in many areas relies exclusively upon discrete microcavities in order to satisfy challenging combinations of ultra-low-loss performance (high cavity-Q-factor) and cavity design requirements. Indeed, finding a microfabrication bridge connecting ultra-high-Q device functions with micro and nanophotonic circuits has been a long-term priority of the microcavity field. Here, an integrated ridge resonator having a record Q factor over 200 million is presented. Its ultra-low-loss and flexible cavity design brings performance that has been the exclusive domain of discrete silica and crytalline microcavity devices to integrated systems. Two distinctly...

  13. Bridging ultra-high-Q devices and photonic circuits

    Yang, Ki Youl; Oh, Dong Yoon; Lee, Seung Hoon; Yang, Qi-Fan; Yi, Xu; Vahala, Kerry
    Optical microcavities are essential in numerous technologies and scientific disciplines. However, their application in many areas relies exclusively upon discrete microcavities in order to satisfy challenging combinations of ultra-low-loss performance (high cavity-Q-factor) and cavity design requirements. Indeed, finding a microfabrication bridge connecting ultra-high-Q device functions with micro and nanophotonic circuits has been a long-term priority of the microcavity field. Here, an integrated ridge resonator having a record Q factor over 200 million is presented. Its ultra-low-loss and flexible cavity design brings performance that has been the exclusive domain of discrete silica and crytalline microcavity devices to integrated systems. Two distinctly...

  14. Complex wavefront engineering with disorder-engineered metasurfaces

    Jang, Mooseok; Horie, Yu; Shibukawa, Atsushi; Brake, Joshua; Liu, Yan; Kamali, Seyedeh Mahsa; Arbabi, Amir; Ruan, Haowen; Faraon, Andrei; Yang, Changhuei
    Recently, complex wavefront engineering with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics. These capabilities include extended volume, aberration-free focusing and subwavelength focusing via evanescent mode coupling. However, translating these capabilities to useful applications has remained challenging as the input-output characteristics of the disordered media (P variables) need to be exhaustively determined via O(P) measurements. Here, we propose a paradigm shift where the disorder is specifically designed so that its exact characteristics are known, resulting in an a priori determined transmission matrix that can be utilized with only a few alignment steps. We implement this concept...

  15. Complex wavefront engineering with disorder-engineered metasurfaces

    Jang, Mooseok; Horie, Yu; Shibukawa, Atsushi; Brake, Joshua; Liu, Yan; Kamali, Seyedeh Mahsa; Arbabi, Amir; Ruan, Haowen; Faraon, Andrei; Yang, Changhuei
    Recently, complex wavefront engineering with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics. These capabilities include extended volume, aberration-free focusing and subwavelength focusing via evanescent mode coupling. However, translating these capabilities to useful applications has remained challenging as the input-output characteristics of the disordered media (P variables) need to be exhaustively determined via O(P) measurements. Here, we propose a paradigm shift where the disorder is specifically designed so that its exact characteristics are known, resulting in an a priori determined transmission matrix that can be utilized with only a few alignment steps. We implement this concept...

  16. Complex wavefront engineering with disorder-engineered metasurfaces

    Jang, Mooseok; Horie, Yu; Shibukawa, Atsushi; Brake, Joshua; Liu, Yan; Kamali, Seyedeh Mahsa; Arbabi, Amir; Ruan, Haowen; Faraon, Andrei; Yang, Changhuei
    Recently, complex wavefront engineering with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics. These capabilities include extended volume, aberration-free focusing and subwavelength focusing via evanescent mode coupling. However, translating these capabilities to useful applications has remained challenging as the input-output characteristics of the disordered media (P variables) need to be exhaustively determined via O(P) measurements. Here, we propose a paradigm shift where the disorder is specifically designed so that its exact characteristics are known, resulting in an a priori determined transmission matrix that can be utilized with only a few alignment steps. We implement this concept...

  17. An Integrated-Photonics Optical-Frequency Synthesizer

    Spencer, Daryl T.; Lee, Seung Hoon; Oh, Dong Yoon; Suh, Myoung-Gyun; Yang, Ki Youl; Vahala, Kerry
    Integrated-photonics microchips now enable a range of advanced functionalities for high-coherence applications such as data transmission, highly optimized physical sensors, and harnessing quantum states, but with cost, efficiency, and portability much beyond tabletop experiments. Through high-volume semiconductor processing built around advanced materials there exists an opportunity for integrated devices to impact applications cutting across disciplines of basic science and technology. Here we show how to synthesize the absolute frequency of a lightwave signal, using integrated photonics to implement lasers, system interconnects, and nonlinear frequency comb generation. The laser frequency output of our synthesizer is programmed by a microwave clock across...

  18. Purcell Enhancement of Parametric Luminescence: Bright and Broadband Nonlinear Light Emission in Metamaterials

    Davoyan, Artur R.; Atwater, Harry A.
    Single-photon and correlated two-photon sources are important elements for optical information systems. Nonlinear downconversion light sources are robust and stable emitters of single photons and entangled photon pairs. However, the rate of downconverted light emission, dictated by the properties of low-symmetry nonlinear crystals, is typically very small, leading to significant constrains in device design and integration. In this paper, we show that the principles for spontaneous emission control (i.e. Purcell effect) of isolated emitters in nanoscale structures, such as metamaterials, can be generalized to describe the enhancement of nonlinear light generation processes such as parametric down conversion. We develop a...

  19. Global modes and nonlinear analysis of inverted-flag flapping

    Goza, Andres; Colonius, Tim; Sader, John E.
    An inverted flag has its trailing edge clamped and exhibits dynamics distinct from that of a conventional flag, whose leading edge is restrained. We perform nonlinear simulations and a global stability analysis of the inverted-flag system for a range of Reynolds numbers, flag masses and stiffnesses. Our global stability analysis is based on a linearisation of the fully-coupled fluid-structure system of equations. The calculated equilibria are steady-state solutions of the fully-coupled nonlinear equations. By implementing this approach, we (i) explore the mechanisms that initiate flapping, (ii) study the role of vortex shedding and vortex-induced vibration (VIV) in large-amplitude flapping, and...

  20. Micro-optical Tandem Luminescent Solar Concentrators

    Needell, David R.; Ilic, Ognjen; Bukowsky, Colton R.; Nett, Zachary; Xu, Lu; He, Junwen; Bauser, Haley; Lee, Benjamin G.; Geisz, John F.; Nuzzo, Ralph G.; Alivisatos, A. Paul; Atwater, Harry A.
    Traditional concentrating photovoltaic (CPV) systems utilize multijunction cells to minimize thermalization losses, but cannot efficiently capture diffuse sunlight, which contributes to a high levelized cost of energy (LCOE) and limits their use to geographical regions with high direct sunlight insolation. Luminescent solar concentrators (LSCs) harness light generated by luminophores embedded in a light-trapping waveguide to concentrate light onto smaller cells. LSCs can absorb both direct and diffuse sunlight, and thus can operate as flat plate receivers at a fixed tilt and with a conventional module form factor. However, current LSCs experience significant power loss through parasitic luminophore absorption and incomplete...

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