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Caltech Authors (130.332 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 56.985

  1. A Tight Relation between N/O Ratio and Galaxy Stellar Mass Can Explain the Evolution of Strong Emission Line Ratios with Redshift

    Masters, Daniel; Faisst, Andreas; Capak, Peter
    The offset of high-redshift star-forming galaxies in the [O III]/Hβ versus [N II]/Hα (O3N2) diagram in comparison with the local star-forming galaxy sequence is now well established. The physical origin of the shift is the subject of some debate and has important implications for metallicity measurements based on strong lines at all redshifts. To investigate the origin of the O3N2 offset, we use a sample of ~100,000 star-forming galaxies from the Sloan Digital Sky Survey DR12 to understand how measurable galaxy physical properties (Σ_(SFR), ionization parameter, nitrogen-to-oxygen (N/O) ratio, and stellar mass) drive galaxy position in two key diagnostic diagrams:...

  2. Enabling high confidence detections of gravitational-wave bursts

    Littenberg, Tyson B.; Kanner, Jonah B.; Cornish, Neil J.; Millhouse, Margaret
    Extracting astrophysical information from gravitational-wave detections is a well-posed problem and thoroughly studied when detailed models for the waveforms are available. However, one motivation for the field of gravitational-wave astronomy is the potential for new discoveries. Recognizing and characterizing unanticipated signals requires data analysis techniques which do not depend on theoretical predictions for the gravitational waveform. Past searches for short-duration unmodeled gravitational-wave signals have been hampered by transient noise artifacts, or “glitches,” in the detectors. We have put forth the BayesWave algorithm to differentiate between generic gravitational-wave transients and glitches, and to provide robust waveform reconstruction and characterization of the...

  3. Metalloproteins : theory, calculations, and experiments

    Preface: Metalloproteins play essential critical functional roles in enzymatically catalyzing reactions difficult to achieve without metals, in signal transduction, and in storage and transport of proteins constituting over 1/3 of the proteome of living organisms. Recent breakthroughs in crystallography have provided insights into understanding their mechanisms, but challenges remain in identifying the particularly redox states of the metals and in the chemical mechanisms for the complex reactions they catalyze. With these advances in structural information, theory and computation are starting to play a more significant role, particularly in identifying the reaction mechanism. This volume summarizes some of the recent progresses...

  4. Systematic U(1)_(B-L) extensions of loop-induced neutrino mass models with dark matter

    Ho, Shu-Yu; Toma, Takashi; Tsumura, Koji
    We study the gauged U(1)_(B–L) extensions of the models for neutrino masses and dark matter. In this class of models, tiny neutrino masses are radiatively induced through the loop diagrams, while the origin of the dark matter stability is guaranteed by the remnant of the gauge symmetry. Depending on how the lepton number conservation is violated, these models are systematically classified. We present complete lists for the one-loop Z_2 and the two-loop Z_3 radiative seesaw models as examples of the classification. The anomaly cancellation conditions in these models are also discussed.

  5. High-resolution and simultaneous measurement along the depth direction using virtual phase conjugation for optical tomography

    Goto, Yuta; Okamoto, Atsushi; Shibukawa, Atsushi; Tomita, Akihisa; Takabayashi, Masanori
    To improve the measurement speed of optical tomography based on the virtual phase conjugation, a virtual measurement position control technique is proposed. Tomographic images were observed with high depth-resolution and high acquisition rate in the numerical simulations.

  6. Structured sampling and recovery of iEEG signals

    Baldassarre, Luca; Aprile, Cosimo; Shoaran, Mahsa; Leblebici, Yusuf; Cevher, Volkan
    Wireless implantable devices capable of monitoring the electrical activity of the brain are becoming an important tool for understanding, and potentially treating, mental diseases such as epilepsy and depression. Compressive sensing (CS) is emerging as a promising approach to directly acquire compressed signals, allowing to reduce the power consumption associated with data transmission. To this end, we propose an efficient CS scheme which exploits the structure of the intracranial EEG signals, both in sampling and recovery. Our structure-aware approach is conceptually simple to implement in hardware and yields state-of-the-art compression rates up to 32× with high reconstruction quality, as illustrated...

  7. Measurement of viscosity of adult zebrafish blood using a capillary pressure-driven viscometer

    Kang, D.; Wang, W.; Lee, J.; Tai, Y. C.; Hsiai, T. K.
    This paper presents the first experimental work on the viscosity measurement of adult zebrafish whole blood using a capillary pressure-driven microfluidic viscometer. After the device calibration with water, the viscosity measurement of human whole blood was performed and in good agreement with published data, demonstrating the reliability of the device. Power law and Carreau-Yasuda rheological models were used to model the non-Newtonian behaviors of the human and zebrafish blood. Theoretical modeling and numerical algorithms were applied to determine the blood viscosity over a wide range of shear rates. The proposed approach is uniquely applicable for small sample volume (down to...

  8. Femtochemistry

    Zewail, Ahmed H.

  9. The microRNA-212/132 cluster regulates B cell development by setting a threshold for Sox4 expression

    Mehta, Arnav; Mann, Mati; Baltimore, David
    MicroRNAs play unique roles as logic elements in B cell differentiation by allowing for fine-tuning of differentiation checkpoints. We have found that the miR-212/132 cluster is induced in B cells in response to anti-IgM stimulation and that it can regulate B cell differentiation by establishing a threshold of Sox4 expression necessary for progression of progenitor B cells. Over-expression of miR-132 blocks the transition of pre-pro-B cells to pro-B cells, in part by inducing apoptosis in primary bone marrow B cells. The deletion of miR-212/132 results in increased B cell output under conditions of inflammatory stress. We validate Sox4 as a...

  10. Immunomodulation of Host Immunity by Bacteriodes fragillis Polysaccharide A (PSA) Prevents Viral Encephalitis

    Chandran, Ramakrishna; Liu, Hiutung; Mazmanian, Sarkis K.; Cantin, Edouard
    A major impact of commensal microbiota on many aspects of host physiology including regulation of host immunity extends beyond the gut to remote sites, including the brain. Studies in mouse models have shown that the commensal Bacteroides fragilis and its capsular PSA can prevent various inflammatory disorders including colitis, experimental autoimmune encephalomyelitis and asthma. However, little is known about the interaction of gut bacteria and their products with the immune system during viral infection. We assessed the immunomodulatory potential of PSA in a murine model of herpes simplex virus (HSV) encephalitis (HSE). Fatal HSE results from inflammation of the brain...

  11. Study of Parylene penetration into microchannel

    Wang, W.; Kang, D.; Tai, Y. C.
    This study reports the penetration properties of various Parylenes (i.e., C, N and HT) inside long microchannels. The work broadly covers the effects of the dimer type, loaded dimer mass, substrate temperature and channel size on the penetration length, i.e., the length that Parylene can be deposited into the microchannel from the inlet. Understanding the mechanism of Parylene penetration into microchannel helps to develop mass-producible inner surface protection design and process for microfluidic devices.

  12. 3D silicon electrodes with built-in glass capillaries for dielectrophoretic single-cell positioning and anaylisis

    Luo, Y.; Yobas, L.
    We present microfluidic designs for dielectrophoretic positioning of single cells and their subsequent analysis based on 3D silicon electrodes featuring built-in capillaries. The designs are presented through numerical simulations as well as experimental validations showing effectiveness of dielectrophoretic forces in trapping single cells. Single-cell experiments are also demonstrated including viability assays and ionophore-mediated intracellular calcium flux assays. Seal resistance measurements between the capillaries and cells trapped, which are essential for patch-clamp assays, are reported.

  13. MEMS for single-islet electroisletogram

    Liu, Y.; Shapero, A.; Zhang, X.; Kang, D.; Park, J.; Xu, L.; Chang, K.; Lin, H.; Ferreri, K.; Tai, Y. C.
    This paper reports the first MEMS device designed for in vitro measuring of electroisletogram (EIG) of individual rat islets. Using vacuum to hold an islet in proximity to a microelectrode, strong EIG signals in millivolt range are obtained, while the noise is about 100μV pk-pk. This work proves the feasibility of using MEMS and EIG for high-throughput screening, in contrast to patch-clamp measurements, of islets for transplantation to treat diabetes.

  14. Experiment on three-dimensional display using spatial cross modulation method with an optical random diffuser

    Sakuma, H.; Okamoto, A.; Shibukawa, A.; Funakoshi, H.; Goto, Y.; Kan, Y.; Tomita, A.
    We performed an experiment on a three-dimensional (3D) display using the spatial cross modulation (SCM) method with a single phase-only spatial light modulator and an optical random diffuser. The experimental result revealed the SCM has great potential to realize the 3D display with unprecedented high resolution and light utilization efficiency.

  15. Systematic Error-Correcting Codes for Permutations and Multi-Permutations

    Buzaglo, Sarit; Yaakobi, Eitan; Etzion, Tuvi; Bruck, Jehoshua
    Multi-permutations and in particular permutations appear in various applications in an information theory. New applications, such as rank modulation for flash memories, have suggested the need to consider error-correcting codes for multi-permutations. In this paper, we study systematic error-correcting codes for multi-permutations in general and for permutations in particular. For a given number of information symbols k, and for any integer t, we present a construction of (k+r,k)systematic t-error-correcting codes, for permutations of length k+r, where the number of redundancy symbols r is relatively small. In particular, for a given t and for sufficiently large k, we obtain r=t+1, while...

  16. Search for gamma-ray emission from AE Aquarii with seven years of FERMI-LAT observations

    Li, Jian; Torres, Diego F.; Rea, Nanda; de Ona Wilhelmi, Emma; Papitto, Alessandro; Hou, Xian; Mauche, Christopher W.
    AE Aquarii (AE Aqr) is a cataclysmic binary hosting one of the fastest rotating (P$_{\rm spin}$ = 33.08 s) white dwarfs known. Based on seven years of Fermi Large Area Telescope (LAT) Pass 8 data, we report on a deep search for gamma-ray emission from AE Aqr. Using X-ray observations from ASCA, XMM-Newton, Chandra, Swift, Suzaku, and NuSTAR, spanning 20 years, we substantially extend and improve the spin ephemeris of AE Aqr. Using this ephemeris, we searched for gamma-ray pulsations at the spin period of the white dwarf. No gamma-ray pulsations were detected above 3 $\sigma$ significance. Neither phase-averaged gamma-ray emission nor gamma-ray variability of AE Aquarii is...

  17. Role of T cell receptors in suppressing HIV infection in elite controllers

    Joglekar, Alok; Lamothe, Pedro A.; Ouyang, Yong; Liu, Zhe; Walker, Bruce D.; Baltimore, David
    Virtually all HIV-infected patients progress to AIDS if not treated. A group of patients, called Elite Controllers (ECs), can suppress HIV infection without treatment. This ability of ECs is, in part, due to potent CD8+ T cell (CTL) responses against HIV epitopes presented by human leukocyte antigen (HLA) molecules. In this study, we focused on CTL responses restricted to HLA-B27, an allele that is enriched in ECs, but is not sufficient for protective ability. In HLA-B27+ ECs or non-controllers (NCs), immunodominant CTL responses specific to the KK10 epitope in Gag are found. Previous studies have shown that unlike NCs, B27-KK10-specific...

  18. Ultrafast Electron Diffraction. 4. Molecular Structures and Coherent Dynamics

    Williamson, J. Charles; Zewail, Ahmed H.
    Ultrafast electron diffraction (UED) is developed, in this and the accompanying paper, as a method for studying gas-phase molecular structure and dynamics on the picosecond (ps) to femtosecond (fs) time scale. Building on our earlier reports (henceforth referred to as 1-3), we discuss theoretical and experimental considerations for the approach. Specifically we show that the use of rotational and vibrational coherences can add a new dimension to structural determination of gas-phase species. In addition to the internuclear separations of the molecular sample, the spatial alignment reflected in the scattering pattern contains bond angles and rotational constants for both excited-state and ground-state species. Vibrational coherence effects are...

  19. Femtosecond Real-Time Probing of Reactions. 16. Dissociation with Intense Pulses

    Materny, A.; Herek, J. L.; Cong, P.; Zewail, A. H.
    In this contribution, we consider the wave packet dynamics in the dissociation reaction of NaI at different laser powers for both the preparation and the probing. The probing is made for the asymptotic Na fragment as well as the transition-state complex [Na•••I]≠*. A novel nonlinear behavior at higher intensities is reported and examined here with a new set of experiments. This behavior reflects the change in the absorption cross section along the reaction coordinate and can be quantified using a simple kinetic picture and a classical model of the dynamics.

  20. Femtosecond Real-Time Probing of Reactions. 15. Time-Dependent Coherent Alignment

    Baskin, J. Spencer; Zewail, Ahmed H.
    The time evolution of product-state anisotropy, through absorption or fluorescence, is developed and compared with the experimental observations for three reactions involving elementary and complex dynamics. The reactions are trans-stilbene-He → trans-stilbene + He, ICN → I + CN, and Hgl_2-Hgl + I. Reagant rotation, applied torque, vibrational averaging, and dynamic axis switching are incorporated into the theoretical treatment. The theory is classical in approach, but it describes the experimental behavior on the femtosecond to picosecond time scale, which enables one to obtain the nature of the angular momentum in the final distribution, the structure of the final fragments, and the geometry of the initial...

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