Repository of works by Caltech published authors.
Type = Book Section
Mostrando recursos 1 - 20 de 3.202
Self-induced polarization anisoplanatism - Breckinridge, James B.
This paper suggests that the astronomical science data recorded with low F# telescopes for applications requiring a known point spread function shape and those applications requiring instrument polarization calibration may be compromised unless the effects of vector wave propagation are properly modeled and compensated. Exoplanet coronagraphy requires “matched filter” masks and explicit designs for the real and imaginary parts for the mask transmittance. Three aberration sources dominate image quality in astronomical optical systems: amplitude, phase and polarization. Classical ray-trace aberration analysis used today by optical engineers is inadequate to model image formation in modern low F# high-performance astronomical telescopes. We...
Optical contamination control in the Advanced LIGO ultra-high
vacuum system - Phelps, Margot H.; Gushwa, Kaitlin E.; Torrie, Calum I.
Fused silica optics in the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors are extremely sensitive to optical scattering and absorption losses induced by both particulate and hydrocarbon contamination. At full power, the optical surfaces are illuminated with up to 200 kW/cm^2. Additionally, the round-trip test mass cavity loss budget is limited to 70 ppm total from all sources. Even low-level contaminants can result in laser damage to optics during the operation the interferometers, and/or the unacceptable reduction of overall detector sensitivity. These risks are mitigated by a two-pronged approach: quantifying contamination sources and the extent of contamination, then reducing sources...
Non-Patent Primary Literature: Journals, Conference Papers, Reports, Abstracts and Preprints - Roth, Dana L.
Successful research efforts, in either academe or industry, require an awareness of the state of the art. This is necessary in order to identify previous research, to develop an understanding of the research problem, and to avoid unnecessary duplication of work. In addition, maintaining an on-going awareness of current literature in your area of chemistry, is crucial to career advancement. This is true for graduate students, whose theses must be based on unique research results, as well as for senior researchers who are able to secure grant funding and pursue exclusive technology rights only for original work.
Commercial Availability, Safety, and Hazards - Roth, Dana L.
The importance of being able to obtain chemicals commercially, being
aware of necessary laboratory precautions, and having access to
hazardous-property information is essential for students and researchers.
This chapter provides commercial availability links to individual
chemical company catalogs and to websites that are linked to multiple
commercial sources. It describes laboratory-safety information resources
and provides hazardous-property information, for both individual
and classes of chemicals, and includes appropriate search techniques.
Information on commercial availability, safety, and hazards is interrelated
in the sense that commercial chemical companies are responsible
for providing Material Safety Data Sheets (MSDSs) for their products.
The MSDS for a substance provides basic physical-property information,
possible hazardous properties, and instructions...
Searching For Polymers - Wrublewski, Donna T.
A polymer is broadly defined as a substance made up of many linked atoms or smaller molecules. Unlike small molecules, polymer properties can vary considerably depending on the method of synthesis, measurement technique, and experimental conditions. As such, knowing additional information about the polymer of interest can be helpful when searching for specific information. This chapter outlines some of this additional information to aid in searching primary literature, and also includes references to secondary compendia where possible.
WISE Discovery of Hyper Luminous Galaxies at z=2-4 and Their
Implications for Galaxy and AGN Evolution - Tsai, Chao-Wei; Einsenhardt, Peter; Wu, Jingwen; Bridge, Carrie; Assef, Roberto; Benford, Dominic; Blain, Andrew; Cutri, Roc; Griffith, Roger L.; Jarrett, Thomas; Lonsdale, Carol; Petty, Sara; Sayers, Jack; Stanford, Adam; Stern, Daniel; Wright, Edward L.; Yan, Lin
On behalf of the WISE Science team, we present the discovery of a class of distant dust-enshrouded galaxies with extremely high luminosity. These galaxies are selected to have extreme red colors in the mid-IR using NASA's Wide-field Infrared Survey Explorer (WISE). They are faint in the optical and near-IR, predominantly at z=2-4, and with IR luminosity > 10^(13)L_☉, making them Hyper-Luminous Infrared Galaxies (HyLIRGs). SEDs incorporating the WISE, Spitzer, and Herschel PACS and SPIRE photometry indicate hot dust dominates the bolometric luminosity, presumably powered by AGN. Preliminary multi-wavelength follow-up suggests that they are different from normal populations in the local...
Tiled Array of Pixelated CZT Imaging Detectors for ProtoEXIST2 and MIRAX-HXI - Hong, Jaesub; Allen, Branden; Grindlay, Jonathan; Rodrigues, Barbara; Ellis, Jon Robert; Baker, Robert; Barthelmy, Scott; Mao, Peter; Miyasaka, Hiromasa; Apple, Jeff
We have assembled a tiled array (220 cm^2) of fine pixel (0.6 mm) imaging CZT detectors for a balloon borne widefield hard X-ray telescope, ProtoEXIST2. ProtoEXIST2 is a prototype experiment for a next generation hard X-ray imager MlRAX-HXI on board Lattes, a spacecraft from the Agencia Espacial Brasilieira. MlRAX will survey the 5 to 200 keV sky of Galactic bulge, adjoining southern Galactic plane and the extragalactic sky with 6' angular resolution. This survey will open a vast discovery space in timing studies of accretion neutron stars and black holes. The ProtoEXIST2 CZT detector plane consists of 64 of 5...
The Nature of Light: What are "Photons"? - Mead, Carver
We are told that our present understanding of physical law was ushered in by the Quantum Revolution, which began around 1900 and was brought to fruition around 1930 with the formulation of modern Quantum Mechanics. The "photon" was supposed to be the centerpiece of this revolution, conveying much of its conceptual flavor. What happened during that period was a rather violent redirection of the prevailing world view in and around physics - a process that has still not settled. In this paper I critically review the evolution of the concepts involved, from the time of Maxwell up to the present...
A Herschel Spectroscopic Survey of Warm Molecular Gas in Local
Luminous Infrared Galaxies - Lu, Nanyao; Xu, C. K.; Gao, Y.; Isaak, K.; Armus, L.; Appleton, P.; Charmandaris, V.; Díaz-Santos, T.; Evans, A.; Howell, J.; Iwasawa, K.; Leech, J.; Lord, S.; Mazzarella, J.; Petric, A.; Sanders, D.; Schulz, B.; Surace, J.; van der Werf, P.; Zhao, Y.
We describe an on-going Herschel 200–700 μm spectroscopic survey of a flux-limited sample of 125 local luminous infrared galaxies (LIRGs), targeting primarily at CO line emission from warm and dense molecular gas. The program will provide important statistical data on the interplay between warm molecular gas, IR luminosity, star formation rate and efficiency, AGN, and the diverse properties of LIRGs. Of the 30 sample galaxies observed so far (18 by us; 12 taken from Herschel archive), about 15% show a dominant or significant hot CO gas component emitting at J > 10, that is likely heated by AGN. The other...
Micro/Nano Patterened Integrated Electrochemical Sensors for Implantable Applications - Mujeeb-U-Rahman, Muhammad; Sencan, Mehmet; Adalian, Dvin; Scherer, Axel
Electrochemical sensors are important candidates for
autonomous integrated sensing applications. Such sensors
can provide accurate and long-term measurements of
multiple analyte for applications in complex environments
e.g. in body fluids. As such sensors are made smaller and
need to be fully integrated, special approaches need to be
taken in order to achieve functional sensitivity, stability,
and longevity. Here, we provide details of CMOS
compatible, integrated design and fabrication of these
sensors on very small scales using micro/nano scale
fabrication and surface modification techniques. We also
present in situ functionalization and novel interface design
techniques. We also provide a comparison between
integrated reference electrodes fabricated using CMOS
compatible fabrication techniques. Finally, we show
examples of sensing...
Distributed active radiation: Terahertz power-generation and beam-steering in CMOS - Sengupta, Kaushik
Silicon technology can potentially create low-cost, integrated solutions at Terahertz frequency ranges. However, there are significant challenges in generating sufficient power at these frequency ranges with devices operating near or above f_(max) and further radiating it directly from the chip with integrated beam-control. In this paper, we review some of our work where we propose a true circuit-electromagnetics co-design approach which removes the artificial partitions among the different levels of abstraction in a conventional system design methodology. In the proposed inverse design approach, we start with the desired radiated THz field and aim to formulate metal surface-currents that could generate...
The quadruple-ridged flared horn: A flexible, multi-octave reflector feed spanning f/0.3 to f/2.5 - Akgiray, Ahmed; Weinreb, Sander; Imbriale, William A.
In this paper, we present four quadruple-ridged flared horn designs achieving 6:1 frequency bandwidth with good match and near-constant beamwidth in E- and D-planes. Nominal 10 dB beamwidths of the designs range from 32 to 115 degrees. Such design flexibility makes the quad-ridge horn a very attractive reflector antenna feed candidate, especially for next generation radio telescopes.
NIR/Optical Selected Local Mergers: Spatial Density and sSFR Enhancement - Xu, C. Kevin
Mergers play important roles in triggering the most active objects in the
universe, including (U)LIRGs and QSOs. However, whether they are also important for
the total stellar mass build-up in galaxies in general is unclear and controversial. Answer
to that question depends on the merger rate and on the average strength of merger
induced star formation. In this talk, I will review studies on spatial density and sSFR
enhancement of local mergers found in NIR/optical selected pair samples. In line with
the current literature on galaxy formation/evolution, special attention will be paid on the
dependence of the local merger rate and the sSFR enhancement on four fundamental
Robust control of uncertain Markov Decision Processes with temporal logic specifications - Wolff, Eric M.; Topcu, Ufuk; Murray, Richard M.
We present a method for designing a robust control policy for an uncertain system subject to temporal logic specifications. The system is modeled as a finite Markov Decision Process (MDP) whose transition probabilities are not exactly known but are known to belong to a given uncertainty set. A robust control policy is generated for the MDP that maximizes the worst-case probability of satisfying the specification over all transition probabilities in this uncertainty set. To this end, we use a procedure from probabilistic model checking to combine the system model with an automaton representing the specification. This new MDP is then...
Optimal placement of energy storage in the grid - Bose, Subhonmesh; Gayme, Dennice F.; Topcu, Ufuk; Chandy, K. Mani
This paper studies the problem of optimally placing large-scale energy storage in power grids with both conventional and wind generation. The solution technique for this infinite horizon problem assumes cyclic demand and generation profiles using a semidefinite relaxation of AC optimal power flow. Changes in storage allocation in the network are studied as a function of total storage budget and transmission line-flow constraints. These questions are investigated using an IEEE benchmark system with various generation portfolios.
Designing games for distributed optimization with a time varying communication graph - Li, Na; Marden, Jason R.
The central goal in multi-agent systems is to engineer a decision making architecture where agents make independent decisions in response to local information while ensuring that the emergent global behavior is desirable with respect to a given system level objective. Our previous work identified a systematic methodology for such a task using the framework of state based games. One core advantage of the approach is that it provides a two step process that can be decoupled by utilizing specific classes of games. Exploiting this decomposition could lead to a rich class of distributed learning algorithm. However, a drawback of our...
On the exactness of convex relaxation for optimal power flow in tree networks - Gan, Lingwen; Li, Na; Topcu, Ufuk; Low, Steven
The optimal power flow problem is nonconvex, and a convex relaxation has been proposed to solve it. We prove that the relaxation is exact, if there are no upper bounds on the voltage, and any one of some conditions holds. One of these conditions requires that there is no reverse real power flow, and that the resistance to reactance ratio is non-decreasing as transmission lines spread out from the substation to the branch buses. This condition is likely to hold if there are no distributed generators. Besides, avoiding reverse real power flow can be used as rule of thumb for...
Scheduling for charging plug-in hybrid electric vehicles - Xu, Yunjian; Pan, Feng
We construct a dynamic stochastic model to study the scheduling problem for battery charging of multiple (possibly a large number of) PHEVs. Our model incorporates the stochasticity in future PHEV arrival process and future renewable generation. The objective of scheduling is to maximize the overall social welfare, which is derived from total customer utility, the electricity cost associated with PHEV charging, and the non-completion penalty for not satisfying PHEVs' charging requests. Through a dynamic programming formulation, we show the Less Laxity and Longer remaining Processing time (LLLP) principle: priority should be given to vehicles that have less laxity and longer...
Branch flow model: Relaxations and convexification - Farivar, Masoud; Low, Steven H.
We propose a branch flow model for the analysis and optimization of mesh as well as radial networks. The model leads to a new approach to solving optimal power flow (OPF) problems that consists of two relaxation steps. The first step eliminates the voltage and current angles and the second step approximates the resulting problem by a conic program that can be solved efficiently. For radial networks, we prove that both relaxation steps are always exact, provided there are no upper bounds on loads. For mesh networks, the conic relaxation is always exact and we characterize when the angle relaxation...
Tree codes improve convergence rate of consensus over erasure channels - Sukhavasi, Ravi Teja; Hassibi, Babak
We study the problem of achieving average consensus between a group of agents over a network with erasure links. In the context of consensus problems, the unreliability of communication links between nodes has been traditionally modeled by allowing the underlying graph to vary with time. In other words, depending on the realization of the link erasures, the underlying graph at each time instant is assumed to be a subgraph of the original graph. Implicit in this model is the assumption that the erasures are symmetric: if at time t the packet from node i to node j is dropped, the...