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Caltech Authors (147.369 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 7.449

  1. The Astrophysics of Star Formation Across Cosmic Time at ≳10 GHz with the Square Kilometre Array

    Murphy, Eric J.; Sargent, Mark T.; Beswick, Rob J.; Dickinson, Clive; Heywood, Ian; Hunt, Leslie K.; Hyunh, Minh T.; Jarvis, Matt; Karim, Alexander; Krause, Marita; Prandoni, Isabella; Seymour, Nicholas; Schinnerer, Eva; Tabatabaei, Fatemeh S.; Wagg, Jeff
    In this chapter, we highlight a number of science investigations that are enabled by the inclusion of Band 5 (4.6-13.8 GHz) for SKA1-MID science operations, while focusing on the astrophysics of star formation over cosmic time. For studying the detailed astrophysics of star formation at highredshift, surveys at frequencies ≳10 GHz have the distinct advantage over traditional ~1.4 GHz surveys as they are able to yield higher angular resolution imaging while probing higher rest frame frequencies of galaxies with increasing redshift, where emission of star-forming galaxies becomes dominated by thermal (free-free) radiation. In doing so, surveys carried out at ≳10 GHz provide...

  2. Extraction and Measurement of NAD(P)+ and NAD(P)H

    Kern, Suzanne E.; Price-Whelan, Alexa; Newman, Dianne K.
    Nicotinamide adenine dinucleotides are critical redox-active substrates for countless catabolic and anabolic reactions. Ratios of NAD+ to NADH and NADP+ to NADPH are therefore considered key indicators of the overall intracellular redox potential and metabolic state. These ratios can be measured in bulk conditions using a highly sensitive enzyme cycling-based colorimetric assay (detection limit at or below 0.05 μM or 1 pmol) following a simple extraction procedure involving solutions of acid and base. Special considerations are necessary to avoid measurement artifacts caused by the presence of endogenous redox-active metabolites, such as phenazines made by diverse Pseudomonas species (see Chapter 25).

  3. Molecular Methods in Geomicrobiology

    Coleman, Maureen L.; Newman, Dianne K.
    In addition to the techniques described in Chapter 8, molecular tools have become increasingly important in the study of the presence, activity, and mechanisms of catalysis by geomicrobial organisms. Today, various molecules (deoxyribonucleic acid [DNA], ribonucleic acid [RNA], protein, and lipids) are used to detect specific geomicrobial agents in situ and make inferences about their metabolic activity. DNA sequencing has become routine, expanding our appreciation of the genetic potential of uncultivated organisms and complex natural communities from the environment. Isotope labeling approaches allow us to measure metabolic activity more directly and to specifically link organisms with geochemical fluxes. Finally, the...

  4. Control of underactuated driftless systems using higher-order averaging theory

    Vela, Patricio A.; Burdick, Joel W.
    This paper applies a recently developed "generalized averaging theory" to construct stabilizing feedback control laws for underactuated driftless systems. These controls exponentialy stabilize in the average; the actual system may orbit around the average. Conditions for which the orbit collapses to the averaged trajectory are given. An example validates the theory, demonstrating its utility.

  5. A general averaging theory via series expansions

    Vela, Patricio A.; Burdick, Joel W.
    This paper generalizes averaging theory to arbitrary order by synthesizing series expansion methods for nonlinear time-varying vector fields and their flows with nonlinear Floquet theory. A companion paper uses these results to construct exponentially stabilizing controllers for underactuated nonlinear systems.

  6. Icemaker^(TM): an excel-based environment for collaborative design

    Parkin, Kevin L. G.; Sercel, Joel C.; Liu, Michael J.; Thunnissen, Daniel P.
    The creative process of team design can be rapid and powerful when focused, yet complex designs, such as spacecrafit, can slow and quench the essential elements of this process. Concurrent Engineering techniques partially address this problem, but a fuller realization of their benefits require an approach centering on the human aspects of teamwork. ICEMaker^(TM) is a Microsoft Excel® based software tool that facilitates closer-to-ideal collaboration within teams employing the new Integrated Concurrent Engineering (ICE) methodology. ICE is a generic approach that emphasizes focused collaborative design in a single-room context, and is now employed at several aerospace organizations to increase the...

  7. Electrolysis-based on-chip dispensing system for ESI-MS

    Xie, Jun; He, Qing; Tai, Yu-Chong; Liu, Jun; Lee, Terry
    We report here an integrated on-chip sample dispensing system for Electrospray Ionization-Mass Spectrometry (ESI-MS) applications. The stand-alone chip includes an electrolysis-based micropump, a passive micro mixer and an ESI nozzle. Operation of the chip doesn't require any external fluidic coupling because the chip is designed to have samples filled, sealed and stored in reservoirs inside the chip before testing. Demonstrated here is a chip with two sample reservoirs and dispensing of the samples is electrically controlled individually. Experimentally, on-chip co-dispensing of two different samples is successfully achieved with a dispensing flow rate about 50 nl/min and a continuous spray for...

  8. Integrated surface-micromachined mass flow controller

    Xie, Jun; Shih, Jason; Tai, Yu-Chong
    An integrated surface-micromachined mass flow controller (MFC) that consists of an electrostatically actuated microvalve and a thermal flow sensor is presented here. With a unique design and utilizing a multilayer Parylene process, the active microvalve and the flow sensor are integrated onto a single chip to perform closed-loop flow control. Sensitivity of the flow sensor is 55 μV/(μ/L/min) for airflow and 12.2 μV/(nL/min) for water. The valve is actuated with a 10 kHz AC signal and an applied pressure of 21 kPa can be sealed with an actuation voltage of 200 V_peak (±200 V). For flow control, both Pulse Width...

  9. Kernel level speculative DSM

    Ţăpuş, Cristian; Smith, Justin D.; Hickey, Jason
    Interprocess communication (IPC) is ubiquitous in today's computing world. One of the simplest mechanisms for IPC is shared memory. We present a system that enhances the System V IPC API to support distributed shared memory (DSM) by using speculations. Speculations provide performance improvements by enabling rollback of overly optimistic speculative executions. This paper describes a speculative total order communication protocol, a speculative sequential consistency model, and a speculative distributed locking mechanism. All these are supported by a mathematical model showing the advantages of speculative execution over traditional execution. Our DSM system is part of the Mojave system, which consists of...

  10. 2-D photonic crystal microcavities

    Scherer, A.; Yoshie, T.; Loncar, M.; Vuckovic, J.; Deppe, D. G.; Okamoto, K.
    We have recently developed photonic crystal nanocavities and lasers from both InGaAsP quantum well and InGaAs/GaAs quantum dot materials. We have explored the design compromises for developing high-Q cavities and developed new geometries for sensitive low-threshold optical switches and spectroscopy sources. In this talk, we will review the design, fabrication and characterization of optical cavities defined within photonic crystals.

  11. Photonic bandgap microcavity devices

    Scherer, A.; Vuckovic, J.; Loncar, M.; Yoshie, T.; Okamoto, K.
    Modern semiconductor microfabrication techniques can be used to define the high quality optical components needed in nanophotonic integrated circuits. Here we show our work on design, fabrication and characterization of ultrasmall lasers, filters, modulators and waveguides in photonic crystals.

  12. Custom-Enabled System Architectures for High End Computing

    Sterling, Thomas; Kogge, Peter
    The US Federal Government has convened a major committee to determine future directions for government sponsored high end computing system acquisitions and enabling research. The High End Computing Revitalization Task Force was inaugurated in 2003 involving all Federal agencies for which high end computing is critical to meeting mission goals. As part of the HECRTF agenda, a multi-day community wide workshop was conducted involving experts from academia, industry, and the national laboratories and centers to provide the broadest perspective on important issues related to the HECRTF purview. Among the most critical issues in establishing future directions is the relative merits...

  13. Ion liquid chromatography on-a-chip with beads-packed parylene column

    He, Qing; Pang, Changlin; Tai, Yu-Chong; Lee, Terry D.
    A parylene-MEMS ion-exchange Liquid Chromatography (LC) chip is presented here. The chip is integrated with microfluidic I/O ports, a separation column, frits/filters, and a conductivity detector. The column is packed with conventional LC stationary phase support materials, i.e. micro-beads with surface functional groups. To withstand high pressure normally encountered in high performance liquid chromatography (HPLC), a self-aligned, channel-anchoring technique is developed to increase the pressure rating of the parylene microfluidic devices from 30 to at least 800psi. On-chip injection, separation and detection of anions in water, with ~25 ppm concentration, have been successfully demonstrated. To our knowledge, this is the...

  14. Remarks on certain new methods for blind identification of FIR channels

    Vaidyanathan, P. P.; Su, Borching
    This paper discusses a number of issues pertaining to blind identification of channels. The basics of blind identification are first discussed and a method called Vandermonde method is presented which is based on elementary linear system principles. Then some remarks are made about precoders with paraunitary antipodal preprocessors. It is argued that such preprocessors usually destroy signal richness which is a necessary feature in blind identification systems.

  15. A model for the condensation of a dusty plasma

    Bellan, P. M.
    A model for the condensation of a dusty plasma is constructed by considering the spherical shielding layers surrounding a dust grain test particle. Since the diameter of the shielding region is smaller than a collision mean free path, the shielding region can be considered as being a collisionless spherical region which is surrounded by an outer collisional region. This collisionless inner region is shown to separate into three concentric layers, each having distinct physics. A collisionless Vlasov model must be used for ions in the inner-most layer and it is shown that the resulting ion density is much smaller than...

  16. Rank minimization and applications in system theory

    Fazel, M.; Hindi, H.; Boyd, S.
    In this tutorial paper, we consider the problem of minimizing the rank of a matrix over a convex set. The rank minimization problem (RMP) arises in diverse areas such as control, system identification, statistics and signal processing, and is known to be computationally NP-hard. We give an overview of the problem, its interpretations, applications, and solution methods. In particular, we focus on how convex optimization can be used to develop heuristic methods for this problem.

  17. An integrated LC-ESI chip with electrochemical-based gradient generation

    Xie, Jun; Shih, Jason; Pang, Changlin; Tai, Yu-Chong; Miao, Yunan; Lee, Terry D.
    This work reports the first on-chip generation of gradient elution using electrochemical pumping, for application in Liquid Chromatography-Electrospray Ionization (LC-ESI). The system consists of Parylene, SU-8 and PDMS parts to create two 3 μL on-chip solvent reservoirs, two electrochemical pumps and an ESI nozzle. Pumping is controlled galvanostatically (i.e., through electrolysis current). At low back pressures, pumping rate can reach 200 nL/min using just 40 μA (power consumption <100 μW). At 80 psi, 200 μA (power consumption <1 mW) is sufficient to deliver fluid at 75 nL/min. Higher electrical currents have been used to increase the flow rate or to...

  18. Designing core-shell 3D photonic crystal lattices for negative refraction

    Chernow, Victoria F.; Ng, Ryan C.; Greer, Julia R.
    We use a plane wave expansion method to define parameters for the fabrication of 3-dimensional (3D) core-shell photonic crystals (PhCs) with lattice geometries that are capable of all-angle negative refraction (AANR) in the midinfrared centered around 8.0 μm. We discuss the dependence of the AANR frequency range on the volume fraction of solid within the lattice and on the ratio of the low index core material to the high index shell material. Following the constraints set by simulations, we fabricate two types of nanolattice PhCs: (1) polymer core-germanium shell and (2) amorphous carbon core-germanium shell to enable experimental observation of...

  19. Indoor wireless channel modeling from 2.4 to 24 GHz using a combined E/H-Plane 2D ray tracing method

    Lu, Dai; Rutledge, David
    Future wireless systems are moving to high frequencies for additional bandwidth and frequency reuse. This makes it very important to have accurate and time-efficient models for system planning. We have previously published measurement results for an indoor channel investigation from 2.4 GHz to 24 GHz. We now propose a new combined E/H-plane 2D ray tracing method. This method includes 2D ray-tracing calculations from both horizontal and vertical sections (E/H-planes). The method predicts loss accurately for both line-of-sight (LOS) and non-line-of-sight (NLOS) paths at five frequency bands from 2.4 GHz to 24 GHz. In addition, it predicts the delay spread for...

  20. Photonic crystal microcavity lasers

    Scherer, A.; Loncar, M.; Maune, Brett; Adams, M.; Yoshie, T.
    By using photonic crystal cavity designs, we have defined ultra-small lasers for optical switching and spectroscopy. Here we describe the design, fabrication, and characterization of these nanocavity lasers.

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