Recursos de colección

Caltech Authors (143.226 recursos)

Repository of works by Caltech published authors.

Type = Report or Paper

1. High Redshift Lyman Limit and Damped Lyman-Alpha Absorbers

Storrie-Lombardi, L. J.; McMahon, R. G.; Irwin, M. J.; Hazard, C.
We have obtained high signal:to:noise optical spectroscopy at 5Å resolution of 27 quasars from the APM z>4 quasar survey. The spectra have been analyzed to create new samples of high redshift Lyman-limit and damped Lyman-ɑ absorbers. These data have been combined with published data sets in a study of the redshift evolution and the column density distribution function for absorbers with logN(HI)≥ 17.5, over the redshift range 0.01 < z < 5. The main results are: Lyman limit systems: The data are well fit by a power law N(z) = N_0(1 + z)^y for the number density per unit redshift. For...

2. Prototyping a valinomycin biosynthesis pathway within a cell-free transcription-translation (TX-TL) system

Zhou, Tiffany
Many natural metabolites have antibacterial, antiviral, or anticancer effects and can be developed into new drugs. However, working with the microorganisms that produce these products can be challenging since they are not as well characterized as a model organism like Escherichia coli. In this paper, we investigate the potential for a cell-free transcription-translation (TX-TL) system to provide a rapid prototyping platform for characterizing new genetic pathways. We use the valinomycin biosynthesis pathway as a test case, and we show successful heterologous expression of the heterodimeric valinomycin synthetase (VlmSyn, Vlm1: 374 kDa and Vlm2: 284 kDa) from Streptomyces tsusimaensis within the...

3. The NuSTAR view of the true Type 2 Seyfert NGC3147

Bianchi, Stefano; Marinucci, Andrea; Matt, Giorgio; Middei, Riccardo; Barcons, Xavier; Bassani, Loredana; Carrera, Francisco J.; La Franca, Fabio; Panessa, Francesca
We present the first NuSTAR observation of a 'true' Type 2 Seyfert galaxy. The 3-40 keV X-ray spectrum of NGC3147 is characterised by a simple power-law, with a standard {\Gamma}~1.7 and an iron emission line, with no need for any further component up to ~40 keV. These spectral properties, together with significant variability on time-scales as short as weeks (as shown in a 2014 Swift monitoring campaign), strongly support an unobscured line-of-sight for this source. An alternative scenario in terms of a Compton-thick source is strongly disfavoured, requiring an exceptional geometrical configuration, whereas a large fraction of the solid angle to the source is filled by a highly ionised...

4. XMM-Newton and NuSTAR simultaneous X-ray observations of IGR J11215-5952

Sidoli, L.; Tiengo, A.; Paizis, A.; Sguera, V.; Lotti, S.; Natalucci, L.
We report the results of an XMM-Newton and NuSTAR coordinated observation of the Supergiant Fast X-ray Transient (SFXT) IGRJ11215-5952, performed on February 14, 2016, during the expected peak of its brief outburst, which repeats every about 165 days. Timing and spectral analysis were performed simultaneously in the energy band 0.4-78 keV. A spin period of 187.0 +/- 0.4 s was measured, consistent with previous observations performed in 2007. The X-ray intensity shows a large variability (more than one order of magnitude) on timescales longer than the spin period, with several luminous X-ray flares which repeat every 2-2.5 ks, some of which simultaneously observed by both satellites. The broad-band (0.4-78...

5. The reflection spectrum of the low-mass X-ray binary 4U 1636-53

Wang, Yanan; Mendez, Mariano; Sanna, Andrea; Altamirano, Diego; Belloni, T. M.
We present 3-79 keV NuSTAR observations of the neutron star low-mass X-ray binary 4U 1636-53 in the soft, transitional and hard state. The spectra display a broad emission line at 5-10 keV. We applied several models to fit this line: A GAUSSIAN line, a relativistically broadened emission line model, KYRLINE, and two models including relativistically smeared and ionized reflection off the accretion disc with different coronal heights, RELXILL and RELXILLLP. All models fit the spectra well, however, the KYRLINE and RELXILL models yield an inclination of the accretion disc of $\sim88\degree$ with respect to the line of sight, which is at odds with the fact that this source...

6. Experimental metrology to obtain thermal phonon transmission coefficients at solid interfaces

Hua, Chengyun; Chen, Xiangwen; Ravichandran, Navaneetha K.; Minnich, Austin J.
Interfaces play an essential role in phonon-mediated heat conduction in solids, impacting applications ranging from thermoelectric waste heat recovery to heat dissipation in electronics. From the microscopic perspective, interfacial phonon transport is described by transmission coefficients that link vibrational modes in the materials composing the interface. However, direct experimental determination of these coefficients is challenging because most experiments provide a mode-averaged interface conductance that obscures the microscopic detail. Here, we report a metrology to extract thermal phonon transmission coefficients at solid interfaces using ab-initio phonon transport modeling and a thermal characterization technique, time-domain thermoreflectance. In combination with transmission electron microscopy characterization...

7. Quantum phases of disordered three-dimensional Majorana-Weyl fermions

Wilson, Justin H.; Pixley, J. H.; Goswami, Pallab; Das Sarma, S.
The gapless Bogoliubov-de Gennes (BdG) quasiparticles of a clean three dimensional spinless p_x + ip_y superconductor provide an intriguing example of a thermal Hall semimetal (ThSM) phase of Majorana-Weyl fermions; such a phase can support a large anomalous thermal Hall conductivity and protected surface Majorana-Fermi arcs at zero energy. We study the effects of quenched disorder on such a gapless topological phase by carrying out extensive numerical and analytical calculations on a lattice model for a disordered, spinless p_x + ip_y superconductor. Using the kernel polynomial method, we compute both average and typical density of states for the BdG quasiparticles,...

8. Refined large N duality for torus knots

Kameyama, Masaya; Nawata, Satoshi
We formulate large N duality of U(N) refined Chern-Simons theory with a torus knot/link in S^3. By studying refined BPS states in M-theory, we provide the explicit form of low-energy effective actions of Type IIA string theory with D4-branes on the Ω-background. This form enables us to relate refined Chern-Simons invariants of a torus knot/link in S^3 to refined BPS invariants in the resolved conifold. Assuming that the extra U(1) global symmetry acts on BPS states trivially, the duality predicts graded dimensions of cohomology groups of moduli spaces of M2-M5 bound states associated to a torus knot/link in the resolved conifold.

9. Bulk Connectedness and Boundary Entanglement

Bao, Ning; Remmen, Grant N.
We prove, for any state in a conformal field theory defined on a set of boundary manifolds with corresponding classical holographic bulk geometry, that for any bipartition of the boundary into two non-clopen sets, the density matrix cannot be a direct product of the reduced density matrices on each region of the bipartition. In particular, there must be entanglement across the bipartition surface. We extend this no-go theorem to general, arbitrary partitions of the boundary manifolds into non-clopen parts, proving that the density matrix cannot be a direct product. This result gives a necessary condition for states to potentially correspond to holographic duals.

10. New Kaluza-Klein Instantons and Decay of AdS Vacua

Ooguri, Hirosi; Spodyneiko, Lev
We construct a generalization of Witten's Kaluza-Klein instanton, where a higher-dimensional sphere (rather than a circle as in Witten's instanton) collapses to zero size and the geometry terminates at a bubble of nothing. We use the solution to exhibit instability of non-supersymmetric AdS_5 vacua in M Theory compactified on positive Kaehler-Einstein spaces, providing a further evidence for the recent conjecture that any non-supersymmetric anti-de Sitter vacuum supported by fluxes must be unstable.

11. A powerful flare from Sgr A* confirms the synchrotron nature of the X-ray emission

Ponti, G.; George, E.; Scaringi, S.; Zhang, S.; Jin, C.; Dexter, J.; Terrier, R.; Clavel, M.; Degenaar, N.; Eisenhauer, F.; Genzel, R.; Gillessen, S.; Goldwurm, A.; Habibi, M.; Haggard, D.; Hailey, C.; Harrison, F. A.; Merloni, A.; Mori, K.; Nandra, K.; Ott, T.; Pfuhl, O.; Plewa, P. M.; Waisberg, I.
We present the first fully simultaneous fits to the NIR and X-ray spectral slope (and its evolution) during a very bright flare from Sgr A⋆, the supermassive black hole at the Milky Way’s center. Our study arises from ambitious multi-wavelength monitoring campaigns with XMMNewton, NuSTAR and SINFONI. The average multi-wavelength spectrum is well reproduced by a broken power-law with ΓN IR = 1.7 ± 0.1 and ΓX = 2.27 ± 0.12. The difference in spectral slopes (∆Γ = 0.57 ± 0.09) strongly supports synchrotron emission with a cooling break. The flare starts first in the NIR with a flat and bright NIR spectrum, while X-ray radiation is...

12. The Achievable Performance of Convex Demixing

McCoy, Michael B.; Tropp, Joel A.
Demixing is the problem of identifying multiple structured signals from a superimposed, undersampled, and noisy observation. This work analyzes a general framework, based on convex optimization, for solving demixing problems. When the constituent signals follow a generic incoherence model, this analysis leads to precise recovery guarantees. These results admit an attractive interpretation: each signal possesses an intrinsic degrees-of-freedom parameter, and demixing can succeed if and only if the dimension of the observation exceeds the total degrees of freedom present in the observation.

13. Structure of the Legionella Dot/Icm type IV secretion system in situ by electron cryotomography

Ghosal, Debnath; Chang, Yi-Wei; Jeong, Kwangcheol C.; Vogel, Joseph P.
Type IV secretion systems (T4SSs) are large macromolecular machines that translocate protein and DNA and are involved in the pathogenesis of multiple human diseases. Here, using electron cryotomography (ECT), we report the in situ structure of the Dot/Icm type IVB secretion system (T4BSS) utilized by the human pathogen Legionella pneumophila. This is the first structure of a type IVB secretion system, and also the first structure of any T4SS in situ. While the Dot/Icm system shares almost no sequence homology with type IVA secretion systems (T4ASSs), its overall structure shows remarkable similarities to two previously imaged T4ASSs, suggesting shared aspects...

14. The Effect of Compositional Context on Synthetic Gene Networks

Yeung, Enoch; Dy, Aaron J.; Martin, Kyle B.; Ng, Andrew H.; Del Vecchio, Domitilla; Beck, James L.; Collins, James J..; Murray, Richard M.
It is well known that synthetic gene expression is highly sensitive to how genetic elements (promoter structure, spacing regions between promoter and cod- ing sequences, ribosome binding sites, etc.) are spatially configured. An important topic that has received far less attention is how the compositional context, or spatial arrangement, of entire genes within a synthetic gene network affects their individual expression levels. In this paper we show, both quantitatively and qualitatively, that compositional context significantly alters transcription levels in synthetic gene networks. We demonstrate that key characteristics of gene induction, such as ultra-sensitivity and dynamic range, strongly depend on compositional...

15. Subsampled Phase Retrieval for On-chip Lensless Holographic Video

Ryu, Donghun; Wang, Zihao; He, Kuan; Horstmeyer, Roarke; Cossairt, Oliver
On-chip holographic video is a convenient way to monitor biological samples simultaneously at high spatial resolution and over a wide field-of-view. However, due to the limited readout rate of digital detector arrays, one often faces a tradeoff between the per-frame pixel count and frame rate of the captured video. In this report, we propose a subsampled phase retrieval (SPR) algorithm to overcome the spatial-temporal trade-off in holographic video. Compared to traditional phase retrieval approaches, our SPR algorithm uses over an order of magnitude less pixel measurements while maintaining suitable reconstruction quality. We use an on-chip holographic video setup with pixel...

16. Hyper-Selective Plasmonic Color Filters

Fleischman, Dagny; Sweatlock, Luke A.; Murakami, Hirotaka; Atwater, Harry
The subwavelength mode volumes of plasmonic filters are well matched to the small size of state-of-the-art active pixels (~ 1 µm) in CMOS image sensor arrays used in portable electronic devices. Typical plasmonic filters exhibit broad (> 100 nm) transmission bandwidths. Dramatically reducing the peak width of filter transmission spectra would allow for the realization of CMOS hyperspectral imaging arrays, which demand the FWHM of transmission peaks to be less than 30 nm. We find that the design of 5 layer metal-insulator-metal-insulator-metal structures gives rise to multi-mode interference phenomena that suppresses spurious transmission features gives rise to a single narrow...

17. Entanglement dynamics in critical random quantum Ising chain with perturbations

Huang, Yichen
We simulate the entanglement dynamics in a critical random quantum Ising chain with generic perturbations using the time-evolving block decimation algorithm. Starting from a product state, we observe super-logarithmic growth of entanglement entropy with time. The numerical result is consistent with the analytical prediction of Vosk and Altman using a real-space renormalization group technique.

18. Detecting continuous gravitational waves with superfluid ^4He

Singh, S.; De Lorenzo, L. A.; Pikovsky, I.; Schwab, K. C.
Direct detection of gravitational waves is opening a new window onto our universe. Here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of super fluid helium-4 parametrically coupled to a superconducting microwave cavity. This narrowband detection scheme can operate at very high Q-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1-1.5 kHz range. The detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. For reasonable experimental parameters, we...

19. Relativistic Disk Reflection in the Neutron Star X-ray Binary XTE J1709-267 with NuSTAR

Ludlam, R. M.; Miller, J. M.; Cackett, E. C.; Degenaar, N.; Bostrom, A. C.
We perform the first reflection study of the soft X-ray transient and Type 1 burst source XTE J1709-267 using NuSTAR observations during its 2016 June outburst. There was an increase in flux near the end of the observations, which corresponds to an increase from $\sim$0.04 L$_{\mathrm{Edd}}$ to $\sim$0.06 L$_{\mathrm{Edd}}$ assuming a distance of 8.5 kpc. We have separately examined spectra from the low and high flux intervals, which were soft and show evidence of a broad Fe K line. Fits to these intervals with relativistic disk reflection models have revealed an inner disk radius of $13.8_{-1.8}^{+3.0}\ R_{g}$ (where $R_{g} = GM/c^{2}$) for the low flux spectrum and \$23.4_{-5.4}^{+15.6}\...

20. Nature of hard X-ray (3-24 keV) detected luminous infrared galaxies in the COSMOS field

Matsuoka, Kenta; Ueda, Yoshihiro
We investigate the nature of far-infrared (70 um) and hard X-ray (3-24 keV) selected galaxies in the COSMOS field detected with both Spitzer and Nuclear Spectroscopic Telescope Array (NuSTAR). By matching the Spitzer-COSMOS catalog against the NuSTAR-COSMOS catalog, we obtain a sample consisting of a hyperluminous infrared galaxy with log(L_IR/L_sun) > 13, 12 ultraluminous infrared galaxies with 12 < log(L_IR/L_sun) < 13, and 10 luminous infrared galaxies with 11 < log(L_IR/L_sun) < 12, i.e., 23 Hy/U/LIRGs in total. Using their X-ray hardness ratios, we find that 12 sources are obscured active galactic nuclei (AGNs) with absorption column densities of N_H > 10^22 cm^-2, including several Compton-thick (N_H ~ 10^24...

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