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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 6.184

  1. Ultrabroadband tunable external-cavity quantum well lasers

    Mehuys, D.; Eng, L.; Mittelstein, M.; Chen, T. R.; Yariv, A.
    The spectral tunability of properly designed quantum well lasers is demonstrated to equal the range of dye lasers. Theoretical and measured gain spectra are presented to support this statement, and stepwise wavelength tuning over a 125 nm span in GaAs/AlGaAs lasers and 175 nm in InGaAs/AlGaAs lasers are shown.

  2. Monolithic Si bolometer array for the Caltech Submillimeter Observatory

    Wang, Ning; Hunter, T. R.; Benford, D. J.; Serabyn, E.; Phillips, T. G.
    We are developing a submillimeter continuum camera for the Caltech Submillimeter Observatory (CSO) located on Mauna Kea. The camera will employ a monolithic Si bolometer array which was developed by Mosley et al. at the NASA Goddard Space Flight Center (GSFC). The camera will be cooled to a temperature of about 300 mK in a ^3He cryostat, and will operate primarily at wavelengths of 350 and 450 micrometers. We plan to use a bolometer array with 1 x 24 directly illuminated pixels, each pixel of dimension 1 x 2 mm^2, which is about half of the F/4 beam size at...

  3. The Slitmask Alignment Tool: robust, efficient, and astronomer-friendly software for aligning multi-object slitmasks

    Kassis, Marc; Wirth, Gregory D.; Phillips, Andrew C.; Steidel, Charles C.
    Multi-object spectroscopy via custom slitmasks is a key capability on three instruments at the W. M. Keck Observatory. Before observers can acquire spectra they must complete a complex procedure to align each slit with its corresponding science target. We developed the Slitmask Alignment Tool (SAT), to replace a complex, inefficient, and error-prone slitmask alignment process that often resulted in lost sky time for novice and experienced observers alike. The SAT accomplishes rapid initial mask alignment, prevents field misidentification, accurately predicts alignment box image locations, corrects for flexure-induced image displacement, verifies the instrument and exposure configuration, and accommodates both rectangular and...

  4. The organization and management of the Virtual Astronomical Observatory

    Berriman, G. Bruce; Hanisch, Robert J.; Lazio, T. Joseph W.; Szalay, Alexander; Fabbiano, Giuseppina
    The U.S. Virtual Astronomical Observatory (VAO has been in operation since May 2010. Its goal is to enable new science through efficient integration of distributed multi-wavelength data. This paper describes the management and organization of the VAO, and emphasizes the techniques used to ensure efficiency in a distributed organization. Management methods include using an annual program plan as the basis for establishing contracts with member organizations, regular communication, and monitoring of processes.

  5. Developments in high-density Cobra fiber positioners for the Subaru Telescope’s Prime Focus Spectrometer

    Fisher, Charles D.; Braun, David F.; Kaluzny, Joel V.; Seiffert, Michael D.; Dekany, Richard G.; Ellis, Richard S.; Smith, Roger M.
    The Prime Focus Spectrograph (PFS) is a fiber fed multi-object spectrometer for the Subaru Telescope that will conduct a variety of targeted surveys for studies of dark energy, galaxy evolution, and galactic archaeology. The key to the instrument is a high density array of fiber positioners placed at the prime focus of the Subaru Telescope. The system, nicknamed “Cobra”, will be capable of rapidly reconfiguring the array of 2394 optical fibers to the image positions of astronomical targets in the focal plane with high accuracy. The system uses 2394 individual “SCARA robot” mechanisms that are 7.7mm in diameter and use...

  6. A Market Approach for Handling Power Emergencies in Multi-Tenant Data Center

    Islam, Mohammad A.; Ren, Xiaoqi; Ren, Shaolei; Wierman, Adam; Wang, Xiaorui
    Power oversubscription in data centers may occasionally trigger an emergency when the aggregate power demand exceeds the capacity. Handling such an emergency requires a graceful power capping solution that minimizes the performance loss. In this paper, we study power capping in a multi-tenant data center where the operator supplies power to multiple tenants that manage their own servers. Unlike owner-operated data centers, the operator lacks control over tenants' servers. To address this challenge, we propose a novel market mechanism based on supply function bidding, called COOP, to financially incentivize and coordinate tenants' power reduction for minimizing total performance loss (quantified...

  7. Lanthanum fluoride nanoparticles for radiosensitization of tumors

    Kudinov, Konstantin; Bekah, Devesh; Cooper, Daniel; Shastry, Sathvik; Hill, Colin; Bradforth, Stephen; Nadeau, Jay
    Dense inorganic nanoparticles have recently been identified as promising radiosensitizers. In addition to dose enhancement through increased attenuation of ionizing radiation relative to biological tissue, scintillating nanoparticles can transfer energy to coupled photosensitizers to amplify production of reactive oxygen species, as well as provide UVvisible emission for optical imaging. Lanthanum fluoride is a transparent material that is easily prepared as nanocrystals, and which can provide radioluminescence at a number of wavelengths through simple substitution of lanthanum ions with other luminescent lanthanides. We have prepared lanthanum fluoride nanoparticles doped with cerium, terbium, or both, that have good spectral overlap with chlorine6...

  8. Highly accurate spatial mode generation using spatial cross modulation method for mode division multiplexing

    Sakuma, Hiroki; Okamoto, Atsushi; Shibukawa, Atsushi; Goto, Yuta; Tomita, Akihisa
    We propose a spatial mode generation technology using spatial cross modulation (SCM) for mode division multiplexing (MDM). The most well-known method for generating arbitrary complex amplitude fields is to display an off-axis computer-generated hologram (CGH) on a spatial light modulator (SLM). However, in this method, a desired complex amplitude field is obtained with first order diffraction light. This critically lowers the light utilization efficiency. On the other hand, in the SCM, the desired complex field is provided with zeroth order diffraction light. For this reason, our technology can generate spatial modes with large light utilization efficiency in addition to high...

  9. Single exosome detection in serum using microtoroid optical resonators

    Su, Judith
    Recently exosomes have attracted interest due to their potential as cancer biomarkers. We report the real time, label‐free sensing of single exosomes in serum using microtoroid optical resonators. We use this approach to assay the progression of tumors implanted in mice by specifically detecting low concentrations of tumor‐derived exosomes. Our approach measures the adsorption of individual exosomes onto a functionalized silica microtoroid by tracking changes in the optical resonant frequency of the microtoroid. When exosomes land on the microtoroid, they perturb its refractive index in the evanescent field and thus shift its resonance frequency. Through digital frequency locking, we are...

  10. Constraining the Population of Compton-Thick AGN and N_H Distribution in the Local Universe

    Annuar, Adlyka; Gandhi, Poshak; Alexander, Dave; Lansbury, George; Harrison, Fiona; Stern, Daniel
    Compton-thick active galactic nuclei (CTAGN) are defined as AGN that are obscured along our line-of-sight by absorbing gas with a column density of N_H ≳ 10^(24) cm^(-2). This is what makes it difficult to identify them at X-ray energies E <; 10 keV, where the direct emission from the AGN is severely absorbed by the obscuring gas. Because of this, a large fraction of the CTAGN population is believed to be missed by current low X-ray energy observations. In this paper, we present updated results from an ongoing project to form the most unbiased census of CTAGN population in the...

  11. Visual Input for Pen-Based Computers

    Munich, Mario E.; Perona, Pietro
    Handwriting may be captured using a video camera, rather than the customary pressure-sensitive tablet. This paper presents a simple system based on correlation and recursive prediction methods that can track the tip of the pen in real time with sufficient spatio-temporal resolution and accuracy to enable handwritten character recognition. The system is tested on a large and heterogeneous set of examples and its performance is compared to that of three human operators and a commercial high-resolution pressure-sensitive tablet.

  12. Camera-based ID Verification by Signature Tracking

    Munich, Mario E.; Perona, Pietro
    A number of vision-based biometric techniques have been proposed in the past for personal identification. We present a novel one based on visual capturing of signatures. This paper describes a system based on correlation and recursive prediction methods that can track the tip of the pen in real time, with sufficient spatio-temporal resolution and accuracy to enable signature verification. Several examples and the performance of the system are shown.

  13. Structure-Independent Visual Motion Control of the Essential Manifold

    Soatto, S.; Perona, P.
    A new framework for visual motion control is described, which consists of formulating the control task on the so-called essential manifold, a "compact" matrix representation of SE(3). Unlike previous image plane control techniques, our method does not require information about the geometric structure (depth) of the scene or target. This allows us to design control laws that are not ill-conditioned when close to zero-disparity configurations. The control relies on a causal motion estimator (called the "essential filter") that identifies recursively an implicit dynamical model with parameters on the essential manifold.

  14. Observability/Identifiability of Rigid Motion under Perspective Projection

    Soatto, Stefano
    The "visual motion estimation" problem concerns the reconstruction of the motion of an object viewed under projection. This paper addresses the feasibility of such a problem when the object is represented as a "rigid" set of point-features in the Euclidean 3D space. We represent rigid motion as a point on the so-called "essential manifold" and show that it is globally observable from perspective projections under some general position conditions. Such conditions hold when the path of the viewer and the visible objects cannot be embedded in a quadric surface of R^3.

  15. A New Geometrical Interpretation of Trilinear Constraints

    Feng, Xiaolin; Bouguet, Jean-Yves; Perona, Pietro
    We give a new geometrical interpretation of the well-known algebraic trilinear constraints used in motion analysis from three views observation. We show that those algebraic equations correspond to depth errors appropriately weighted by a function of the relative reliability of the corresponding measurements. Therefore directly minimizing the algebraic trilinear equations, in the least squares sense, is a strategy that works well for estimating motion. In addition, we propose a new scheme for recovering the scale factor for motion estimation that is very insensitive to input noise. All our theoretical statements are supported by experimental results.

  16. Classification of Human Motion into Dynamics Based Primitives with Application to Drawing Tasks

    Del Vecchio, D.; Murray, R. M.; Perona, P.
    We develop the study of primitives of human motion, which we refer to as movemes. The idea is to understand human motion by decomposing it into a sequence of elementary building blocks that belong to a known alphabet of dynamical systems. How can we construct an alphabet of movemes from human data? In this paper we address this issue by introducing the notion of well-posednes. Using examples from human drawing data, we show that the well-posedness notion can be applied in practice so to establish if sets of actions, viewed as signals in time, can define movemes.

  17. Studies of Wavelength-Shifting Liquid Filled Quartz Capillaries for Use in a Proposed CMS Calorimeter

    Baumbaugh, B.; Bornheim, A.; Newman, H. B.; Spiropulu, M.; Yang, F.; Zhang, L.; Zhu, R. Y.
    Studies have been done and continue on the design and construction of a Shashlik detector using Radiation hard quartz capillaries filled with wavelength shifting liquid to collect the scintillation light from LYSO crystals for use as a calorimeter in the Phase II CMS upgrade at CERN. The work presented here focuses on the studies of the capillaries and liquids that would best suit the purpose of the detector. Comparisons are made of various liquids, concentrations, and capillary construction techniques will be discussed.

  18. Studies towards a precision timing calorimeter for high energy physics collider experiments

    Anderson, Dustin; Apresyan, Artur; Bornheim, Adolf; Duarte, Javier; Peña, Cristián; Ronzhin, Anatoly; Spiropulu, Maria; Trevor, Jason; Xie, Si
    Current and future high energy physics particle colliders are capable to provide instantaneous luminosities of 10^(34)cm^(−2)s^(−1) and above. The high center of mass energy, the large number of simultaneous collision of beam particles in the experiments and the very high repetition rates of the collision events pose huge challenges. They result in extremely high particle fluxes, causing very high occupancies in the particle physics detectors operating at these machines. To reconstruct the physics events, the detectors have to make as much information as possible available on the final state particles. We briefly discuss how timing information with a precision of...

  19. Discrete, Vorticity-Preserving, and Stable Simplicial Fluids

    Elcott, Sharif; Tong, Yiying; Kanso, Eva; Schröder, Peter; Desbrun, Mathieu
    Visual accuracy, low computational cost, and numerical stability are foremost goals in computer animation. An important ingredient in achieving these goals is the conservation of fundamental motion invariants. For example, rigid or deformable body simulation have benefited greatly from conservation of linear and angular momenta. In the case of fluids, however, none of the current techniques focuses on conserving invariants, and consequently, they often introduce a visually disturbing numerical diffusion of vorticity. Visually just as important is the resolution of complex simulation domains. Doing so with regular (even if adaptive) grid techniques can be computationally delicate. In this chapter, we propose a...

  20. Building your own DEC at home

    Elcott, Sharif; Schröder, Peter
    The methods of Discrete Exterior Calculus (DEC) have given birth to many new algorithms applicable to areas such as fluid simulation, deformable body simulation, and others. Despite the (possibly intimidating) mathematical theory that went into deriving these algorithms, in the end they lead to simple, elegant, and straightforward implementations. However, readers interested in implementing them should note that the algorithms presume the existence of a suitable simplicial complex data structure. Such a data structure needs to support local traversal of elements, adjacency information for all dimensions of simplices, a notion of a dual mesh, and all simplices must be oriented. Unfortunately, most publicly...

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