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Caltech Authors (132.208 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 57.157

  1. Measurement of tt production with additional jet activity, including b quark jets, in the dilepton decay channel using pp collisions at √s = 8 TeV

    Khachatryan, V.; Anderson, D.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Pierini, M.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    Jet multiplicity distributions in top quark pair (tt) events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set corresponding to an integrated luminosity of 19.7fb^(-1). The measurement is performed in the dilepton decay channels (e^+e^−, μ^+μ^−, and e^±μ^∓). The absolute and normalized differential cross sections for tt production are measured as a function of the jet multiplicity in the event for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. The differential ttb and ttbb cross sections are presented for the...

  2. Robust Ambulance Allocation Using Risk-based Metrics

    Krishnan, Kaushik; Marla, Lavanya; Yue, Yisong
    This paper focuses on robust location strategies for a fleet of ambulances in cities in order to maximize service levels under unexpected demand patterns. Our work is motivated by the fact that when small parts of networks incur emergencies according to a heavy-tailed distribution, the structure of the network under resource constraints results in the entire system behaving in a heavy-tailed manner. To address this, metrics other than average-case need to be used. We achieve robust location strategies by including risk metrics that account for tail behavior and not average performance alone. Because of the exponentially large solution space for...

  3. VIP: Joint Traffic Engineering and Caching in Named Data Networks

    Yeh, Edmund; Ho, Tracey; Cui, Ying; Burd, Michael; Liu, Ran; Leong, Derek
    Emerging information-centric networking architectures seek to optimally utilize both bandwidth and storage for efficient content distribution. This highlights the need for joint design of traffic engineering and caching strategies. We present a systematic framework for joint dynamic interest request forwarding and dynamic cache placement and eviction, within the context of the Named Data Networking (NDN) architecture. The framework employs a virtual control plane which operates on the user demand rate for data objects in the network, and an actual plane which handles Interest Packets and Data Packets. We develop distributed algorithms within the virtual plane to achieve network load balancing...

  4. A study of polar codes for MLC NAND flash memories

    Li, Yue; Alhussien, Hakim; Haratsch, Erich F.; Jiang, Anxiao (Andrew)
    The increasing density of NAND flash memories makes data more prone to errors due to severe process variations and disturbance. The urgency to improve NAND flash reliability encourages searching for optimal channel coding methods. This paper reports our efforts towards a read channel for flash memories using polar coding. Our contributions include the solutions to several challenges raised when applying polar codes to NAND flash memories in practice. We propose efficient schemes for shortening both non-systematic and systematic polar codes, making polar codewords be easily adapted to flash page of any size. We demonstrate that the decoding performance of the...

  5. Optimizing Energy Storage Participation in Emerging Power Markets

    Chen, Hao; Liu, Zhenhuan; Coskun, Ayse K.; Wierman, Adam
    The growing amount of intermittent renewables in power generation creates challenges for real-time matching of supply and demand in the power grid. Emerging ancillary power markets provide new incentives to consumers (e.g., electrical vehicles, data centers, and others) to perform demand response to help stabilize the electricity grid. A promising class of potential demand response providers includes energy storage systems (ESSs). This paper evaluates the benefits of using various types of novel ESS technologies for a variety of emerging smart grid demand response programs, such as regulation services reserves (RSRs), contingency reserves, and peak shaving. We model, formulate and solve...

  6. Visual statistical learning produces implicit and explicit knowledge about temporal order information and scene chunks: Evidence from direct and indirect measures

    Otsuka, Sachio; Koch, Christof; Saiki, Jun
    We examined whether visual statistical learning (VSL) produced implicit and/or explicit knowledge about temporal order information and scene chunks, using a rapid serial visual presentation target detection task and a two-alternative forced-choice (2AFC) familiarity test as indirect and direct measures of VSL, respectively. In the familiarization phase, participants viewed a visual stream of natural scenes consisting of four triplets (i.e., three images that always appeared in the same order). In the subsequent target detection task, participants were required to detect target items embedded in a stream of 12 images or 12 words representing each natural scene. In the final 2AFC...

  7. Connecting Automatic Generation Control and Economic Dispatch From an Optimization View

    Li, Na; Zhao, Changhong; Chen, Lijun
    Automatic generation control (AGC) regulates mechanical power generation in response to load changes through local measurements. Its main objective is to maintain system frequency and keep energy balanced within each control area in order to maintain the scheduled net interchanges between control areas. The scheduled interchanges as well as some other factors of AGC are determined at a slower time scale by considering a centralized economic dispatch (ED) problem among different generators. However, how to make AGC more economically efficient is less studied. In this paper, we study the connections between AGC and ED by reverse engineering AGC from an...

  8. Measurement of inclusive jet production and nuclear modifications in pPb collisions at √sNN = 5.02 TeV

    Khachatryan, V.; Anderson, D.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.
    Inclusive jet production in pPb collisions at a nucleon–nucleon (NN) center-of-mass energy of √sNN = 5.02 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 30.1 nb^(−1) is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range −2.0 < ηCM < 1.5 in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about η CM = 0 is observed in the measured kinematic range. The measurements in the pPb system are compared to reference...

  9. Distortion-Power Trade-Offs in Quasi-Stationary Source Transmission over Delay and Buffer Limited Block Fading Channels

    Joda, Roghayeh; Lahouti, Farshad; Erkip, Elza
    This paper investigates distortion-power tradeoffs in transmission of quasi-stationary sources over delay and buffer limited block fading channels by studying encoder and decoder buffering techniques to smooth out the source and channel variations. Four source and channel coding schemes that consider buffer and power constraints are presented to minimize the reconstructed source distortion. The first one is a high performance scheme, which benefits from optimized source and channel rate adaptation. In the second scheme, the channel coding rate is fixed and optimized along with transmission power with respect to channel and source variations; hence this scheme enjoys simplicity of implementation....

  10. Characterization of Ti-Beta zeolites and their reactivity for the photocatalytic reduction of CO_2 with H_2O

    Ikeue, Keita; Yamashita, Hiromi; Takewaki, Takahiko; Davis, Mark E.; Anpo, Masakazu
    A characterization of Ti-Beta zeolites synthesized under various conditions as well as an investigation of their photocatalytic properties for the reduction of CO_2 with H_2O at 323 K to produce CH_4 and CH_3OH were carried out. In situ XAFS spectra measurements indicated that a highly dispersed tetrahedral titanium oxide species was present in the zeolite framework and an increase in the coordination number of the titanium oxide species by the addition of H_2O and CO_2 molecules could be detected. The Ti-Beta zeolite having a hydrophilic property (Ti-Beta(OH)) exhibited a more dramatic increase in the coordination number than the Ti-Beta(F) zeolite...

  11. Mo K- and L-edge X-ray absorption spectroscopic study of the ADP·AlF_4^−-stabilized nitrogenase complex: comparison with MoFe protein in solution and single crystal

    Corbett, Mary C.; Tezcan, F. Akif; Einsle, Oliver; Walton, Mika Y.; Rees, Douglas C.; Latimer, Matthew J.; Hedman, Britt; Hodgson, Keith O.
    The utility of using X-ray absorption spectroscopy (XAS) to study metalloproteins and, specifically, the enzyme complex nitrogenase, is highlighted by this study comparing both the structural and Mo-localized electronic features of the iron-molybdenum cofactor (FeMoco) in isolated MoFe protein and in the ADP·AlF_4^--stabilized complex of the MoFe protein with the Fe protein. No major differences are found at Mo between the two protein forms. The excellent quality of the data at both the Mo K and L edges will provide a baseline for analysis of other intermediates in the nitrogenase cycle. A new capability to delineate various contributions in the...

  12. UHF Deployable Helical Antennas for CubeSats

    Costantine, Joseph; Tawk, Youssef; Maqueda, Ignacio; Sakovsky, Maria; Olson, Gina; Pellegrino, Sergio; Christodoulou, Christos G.
    The design process and the deployment mechanism of a quadrifilar helix antenna (QHA) and a conical log spiral antenna (CLSA) are presented. The two antennas are proposed to operate in the UHF frequency band. They are composed of conductors that are embedded and supported by innovative structural techniques. This allows efficient folding, packaging, and deployment once in space. The conductors in the QHA are composed of beryllium copper and are supported by helical arms of S_2 glass fiber reinforced epoxy. The CLSA, on the other hand, has conductors that are made out of a mesh of phosphor bronze and incorporated...

  13. A Comparison of the Determination of Closure Phase in Optical Interferometry with Fully Filled Apertures and Non-Redundant Aperture Masks

    Readhead, A. C. S.

  14. Density Functional Theory Study of the Geometry, Energetics, and Reconstruction Process of Si(111) Surfaces

    Solares, Santiago D.; Dasgupta, Siddharth; Schultz, Peter A.; Kim, Yong-Hoon; Musgrave, Charles B.; Goddard, William A.
    We report the structures and energies from first principles density functional calculations of 12 different reconstructed (111) surfaces of silicon, including the 3 × 3 to 9 × 9 dimer−adatom−stacking fault (DAS) structures. These calculations used the Perdew−Burke−Ernzerhof generalized gradient approximation of density functional theory and Gaussian basis functions. We considered fully periodic slabs of various thicknesses. We find that the most stable surface is the DAS 7 × 7 structure, with a surface energy of 1.044 eV/1 × 1 cell (1310 dyn/cm). To analyze the origins of the stability of these systems and to predict energetics for more complex,...

  15. μ-p scattering and the glue fraction of the proton

    Politzer, H. David
    The QCD version of the energy-momentum sum rule is tested against SLAC electroproduction and FNAL muon-proton scattering data. While providing only a single number for each Q2, the energy momentum sum rule is significant because the scaling violations due to gluons can be well determined. In particular, gluons carry 30±8% of the proton's energy-momentum at Q2=3.5 GeV2 (which means 22% at 1 GeV2). The largest single corrections of previous estimates of the glue fraction is the inclusion of gluon bremsstrahlung effects. Agreement with experiment is within the uncertainties in the μ-p data. However, the sum rule does not give a...

  16. Gluon corrections to Drell-Yan processes

    Politzer, H. David
    Assuming that the Drell-Yan picture is approximately valid, I compute the O(g^2) gluon radiative corrections in QCD. The corrections are self-consistent, i.e. they satisfy several non-trivial constraints necessary for the validity of the whole picture. There are logarithmic scaling violations in the quark distribution functions, precisely equal to those found in electroproduction. Large transverse momenta (of order of the c.m. energy) are produced, balanced by radiation in the opposite direction. I compute the transverse momentum differential cross section for μ pairs as an example

  17. Measurement of the differential cross sections for top quark pair production as a function of kinematic event variables in pp collisions at √s = 7 and 8 TeV

    Khachatryan, V.; Anderson, D.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Pierini, M.; Spiropulu, M.; Vlimant, J. R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
    Measurements are reported of the normalized differential cross sections for top quark pair production with respect to four kinematic event variables: the missing transverse energy; the scalar sum of the jet transverse momentum (p_T); the scalar sum of the p_T of all objects in the event; and the p T of leptonically decaying W bosons from top quark decays. The data sample, collected using the CMS detector at the LHC, consists of 5.0  fb^(−1) of proton-proton collisions at √s=7  TeV and 19.7  fb^(−1) at √s=8  TeV. Top quark pair events containing one electron or muon are selected. The results are presented after correcting for...

  18. The Star Formation Rate Efficiency of Neutral Atomic-dominated Hydrogen Gas in the Outskirts of Star-forming Galaxies from z ~ 1 to z ~ 3

    Rafelski, Marc; Gardner, Jonathan P.; Fumagalli, Michele; Neeleman, Marcel; Teplitz, Harry I.; Grogin, Norman; Koekemoer, Anton M.; Scarlata, Claudia
    Current observational evidence suggests that the star formation rate (SFR) efficiency of neutral atomic hydrogen gas measured in damped Lyα systems (DLAs) at z ~ 3 is more than 10 times lower than predicted by the Kennicutt–Schmidt (KS) relation. To understand the origin of this deficit, and to investigate possible evolution with redshift and galaxy properties, we measure the SFR efficiency of atomic gas at z ~ 1, z ~ 2, and z ~ 3 around star-forming galaxies. We use new robust photometric redshifts in the Hubble Ultra Deep Field to create galaxy stacks in these three redshift bins, and...

  19. Neural mechanisms and personality correlates of the sunk cost effect

    Fujino, Junya; Fujimoto, Shinsuke; Kodaka, Fumitoshi; Camerer, Colin F.; Kawada, Ryosaku; Tsurumi, Kosuke; Tei, Shisei; Isobe, Masanori; Miyata, Jun; Sugihara, Genichi; Yamada, Makiko; Fukuyama, Hidenao; Murai, Toshiya; Takahashi, Hidehiko
    The sunk cost effect, an interesting and well-known maladaptive behavior, is pervasive in real life, and thus has been studied in various disciplines, including economics, psychology, organizational behavior, politics, and biology. However, the neural mechanisms underlying the sunk cost effect have not been clearly established, nor have their association with differences in individual susceptibility to the effect. Using functional magnetic resonance imaging, we investigated neural responses induced by sunk costs along with measures of core human personality. We found that individuals who tend to adhere to social rules and regulations (who are high in measured agreeableness and conscientiousness) are more...

  20. CLASH-VLT: Dissecting the Frontier Fields Galaxy Cluster MACS J0416.1-2403 with ∼800 Spectra of Member Galaxies

    Balestra, I.; Medezinski, E.; Zitrin, A.
    We present VIMOS-Very Large Telescope (VLT) spectroscopy of the Frontier Fields cluster MACS J0416.1-2403 (z = 0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts over ~600 arcmin^2, including ~800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to ~2.2 r _(200) (~4 Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster (M _(200) ~ 0.9 × 10^(15) M_⊙ and σ_(V,r200) ~ 1000 km s^(−1)) presenting...

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