Sunday, January 31, 2016

 

 



Soy un nuevo usuario

Olvidé mi contraseña

Entrada usuarios

Lógica Matemáticas Astronomía y Astrofísica Física Química Ciencias de la Vida
Ciencias de la Tierra y Espacio Ciencias Agrarias Ciencias Médicas Ciencias Tecnológicas Antropología Demografía
Ciencias Económicas Geografía Historia Ciencias Jurídicas y Derecho Lingüística Pedagogía
Ciencia Política Psicología Artes y Letras Sociología Ética Filosofía
 

rss_1.0 Recursos de colección

Caltech Authors (119,427 recursos)
Repository of works by Caltech published authors.

Type = Report or Paper

Mostrando recursos 1 - 20 de 3,349

1. Luminous blue variables: An imaging perspective on their binarity and near environment - Martayan, Christophe; Lobel, Alex; Baade, Dietrich; Mehner, Andrea; Rivinius, Thomas; Boffin, Henri M. J.; Girard, Julien; Mawet, Dimitri; Montagnier, Guillaume; Blomme, Ronny; Kervella, Pierre; Sana, Hugues; Štefl, Stanislav; Zorec, Juan; Lacour, Sylvestre; Le Bouquin, Jean-Baptiste; Martins, Fabrice; Mérand, Antoine; Patru, Fabien; Selman, Fernando; Frémat, Yves
Luminous blue variables (LBVs) are rare massive stars with very high luminosity. They are characterized by strong photo-metric and spectroscopic variability related to transient eruptions. The mechanisms at the origin of these eruptions is not well known. In addition, their formation is still problematic and the presence of a companion could help to explain how they form. Aims. This article presents a study of seven LBVs (about 20% of the known Galactic population), some Wolf-Rayet stars, and massive binaries. We probe the environments that surround these massive stars with near-, mid-, and far-infrared images, investigating potential nebula/shells and the companion stars. Methods. To investigate large spatial scales, we used...

2. Ejection of the massive Hydrogen-rich envelope timed with the collapse of the stripped SN2014C - Margutti, Raffaella; Kamble, A.; Milisavljevic, D.; de Mink, S. E.; Zapartas, E.; Drout, M. R.; Chornock, R.; Risaliti, G.; Zauderer, B. A.; Bietenholz, M.; Cantiello, M.; Chakraborti, S.; Chomiuk, L.; Fong, W.; Grefenstette, B. W.; Guidorzi, C.; Kirshner, R. P.; Parrent, J. T.; Patnaude, D.; Soderberg, A. M.; Gehrels, N. C.; Harrison, F. A.
We present multi-wavelength observations of SN2014C during the first 500 days. These observations represent the first solid detection of a young extragalactic stripped-envelope SN out to high-energy X-rays. SN2014C was the explosion of an H-stripped progenitor star with ordinary explosion parameters. However, over the time scale of ~1yr, SN2014C experienced a complete metamorphosis and evolved from an ordinary H-poor supernova of type Ib into a strongly interacting, H-rich supernova of type IIn. Signatures of the SN shock interacting with a dense medium are observed across the spectrum. Coordinated observations with Swift, Chandra and NuSTAR have captured the evolution in detail and revealed the presence of a massive shell of...

3. The LSST Data Management System - Jurić, Mario; Dubois-Felsmann, Gregory; Ciardi, David R.; Van Dyk, Schuyler D.
The Large Synoptic Survey Telescope (LSST; Ivezić et al. 2008) is a large-aperture, wide-field, ground-based survey system that will image the sky in six optical bands from 320 to 1050 nm, uniformly covering approximately 18,000 deg^2 of the sky over 800 times. The LSST is currently under construction on Cerro Pachón in Chile, and expected to enter operations in 2022. Once operational, the LSST will explore a wide range of astrophysical questions, from discovering “killer” asteroids to examining the nature of Dark Energy. The LSST will generate on average 15 TB of data per night, and will require a comprehensive Data...

4. Type II supernova energetics and comparison of light curves to shock-cooling models - Rubin, Adam; Kulkarni, S. R.; Perley, Daniel A.; Cao, Yi
During the first few days after explosion, Type II supernovae (SNe) are dominated by relatively simple physics. Theoretical predictions regarding early-time SN light curves in the ultraviolet (UV) and optical bands are thus quite robust. We present, for the first time, a sample of 57 R-band Type II SN light curves that are well monitored during their rise, having > 5 detections during the first 10 days after discovery, and a well-constrained time of explosion to within 1-3 days. We show that the energy per unit mass (E/M) can be deduced to roughly a factor of five by comparing early-time optical...

5. A Systematic Study of Mid-Infrared Emission from Core-Collapse Supernovae with SPIRITS - Tinyanont, Samaporn; Kasliwal, Mansi M.; Fox, Ori D.; Lau, Ryan; Smith, Nathan; Williams, Robert; Jencson, Jacob; Perley, Daniel; Dykhoff, Devin; Gehrz, Robert; Johansson, Joel; Van Dyk, Schuyler D.; Masci, Frank; Cody, Ann Marie; Prince, Tom
We present a systematic study of mid-infrared (mid-IR) emission from 141 nearby supernovae (SNe) observed with the InfraRed Array Camera (IRAC) on the Spitzer Space Telescope. These SNe reside in one of the 190 galaxies within 20Mpc drawn from the ongoing three-year SPIRITS program. Both new SPIRITS observations and data from other programs available in the archive are used in this study. We detect 8 Type Ia SNe and 36 core-collapse SNe. All Type I SNe fade and become undetectable within 3 years of explosion. About 22±11% of Type II SNe continue to be detected at late-times with five events...

6. An Intermediate Type Ia Supernova Between Normal And Super-Chandrasekhar - Cao, Yi; Johansson, J.; Nugent, Peter E.; Goobar, A.; Nordin, Jakob; Kulkarni, S. R.; Cenko, S. Bradley; Fox, Ori; Kasliwal, Mansi M.; Fremling, C.; Amanullah, R.; Hsiao, E. Y.; Perley, D. A.; Bue, Brian D.; Masci, Frank J.; Lee, William H.; Chotard, Nicolas
While recent observations provide evidence that super-Chandrasekhar Type Ia supernovae and at least a fraction of normal Type Ia supernovae probably originate from double-degenerate systems, these two subclasses show distinct characteristics observationally. Here we report an intermediate supernova iPTF13asv that may bridge this gap. On the one hand, similar to normal Type Ia supernovae, the over-luminous iPTF13asv follows the empirical relation between the peak magnitude, the lightcurve shape and its intrinsic color, and shows a near-IR secondary maximum like normal supernovae. On the other hand, similar to super-Chandrasekhar events, it has strong UV emission around maximum, low expansion velocities and persistent...

7. Radio observations of a sample of broad-lined type Ic supernovae discovered by PTF/iPTF: A search for relativistic explosions - Corsi, A.; Gal-Yam, A.; Kulkarni, S. R.; Frail, D. A.; Mazzali, P. A.; Cenko, S. B.; Kasliwal, M. M.; Cao, Y.; Horesh, A.; Palliyaguru, N.; Perley, D. A.; Laher, R. R.; Taddia, F.; Leloudas, G.; Maguire, K.; Nugent, P. E.; Sollerman, J.; Sullivan, M.
Long duration y-ray bursts are thought to be a rare subclass of stripped-envelope core-collapse supernovae that launch collimated relativistic out ows (jets). All y-ray-burst-associated supernovae are spectroscopically of Type Ic with broad lines, but the fraction of broad-lined Type Ic supernovae harboring low-luminosity y-ray-bursts remains largely unconstrained. Some supernovae should be accompanied by off-axis y-ray burst jets that remain invisible initially, but then emerge as strong radio sources (as the jets decelerate). However, this critical prediction of the jet model for y-ray bursts has yet to be verified observationally. Here, we present K. G. Jansky Very Large Array radio observations of...

8. Flash Spectroscopy: Emission Lines from the Ionized Circumstellar Material around <10-Day-Old Type II Supernovae - Khazov, D.; Kulkarni, S. R.; Kasliwal, M. M.; Cao, Y.; Perley, D.; Laher, R. R.; Surace, J.
Supernovae (SNe) embedded in dense circumstellar material (CSM) may show prominent emission lines in their early-time spectra (≤ 10 days after the explosion), owing to recombination of the CSM ionized by the shock-breakout flash. From such spectra (“flash spectroscopy”), we can measure various physical properties of the CSM, as well as the mass-loss rate of the progenitor during the year prior to its explosion. Searching through the Palomar Transient Factory (PTF and iPTF) SN spectroscopy databases from 2009 through 2014, we found 12 Type II SNe showing flash-ionized (FI) signatures in their first spectra. All are younger than 10 days. These...

9. Positive Signs in Massive Gravity - Cheung, Clifford; Remmen, Grant N.
We derive new constraints on massive gravity from unitarity and analyticity of scattering amplitudes. Our results apply to a general effective theory defined by Einstein gravity plus the leading soft diffeomorphism-breaking corrections. We calculate scattering amplitudes for all combinations of tensor, vector, and scalar polarizations. The high-energy behavior of these amplitudes prescribes a specific choice of couplings that ameliorates the ultraviolet cutoff, in agreement with existing literature. We then derive consistency conditions from analytic dispersion relations, which dictate positivity of certain combinations of parameters appearing in the forward scattering amplitudes. These constraints exclude all but a small island in the parameter space of ghost-free massive gravity. While the theory of...

10. Effective Field Theory of 2D van Hove Singularities - Kapustin, Anton; McKinney, Tristan; Rothstein, Ira Z.
We study the effective field theory of 2D fermions with a short-range interaction in the presence of a van Hove singularity. We find that there are additional divergences associated with the singularity that necessitate regularization beyond the usual Wilsonian cut-off. In the full theory these divergences are cut off by the finite size of the Brillouin zone. This leads to a UV/IR mixing and causes the RG equation for the coupling constant to have an explicit dependence on the ratio of the Wilsonian cut-off to the bandwidth. We discuss the properties of the superconducting ground state and the transport properties of the normal state and show that the...

11. Duplication-Correcting Codes for Data Storage in the DNA of Living Organisms - Jain, Siddharth; Farnoud, Farzad; Schwartz, Moshe; Bruck, Jehoshua
The ability to store data in the DNA of a living organism has applications in a variety of areas including synthetic biology and watermarking of patented genetically-modified organisms. Data stored in this medium is subject to errors arising from various mutations, such as point mutations, indels, and tandem duplication, which need to be corrected to maintain data integrity. In this paper, we provide error-correcting codes for errors caused by tandem duplications, which create a copy of a block of the sequence and insert it in a tandem manner, i.e., next to the original. In particular, we present two families of codes for...

12. The Caltech-NRAO Stripe 82 Survey (CNSS) Paper I: The Pilot Radio Transient Survey In 50 deg^2 - Mooley, K. P.; Hallinan, G.; Bourke, S.; Horesh, A.; Myers, S. T.; Frail, D. A.; Kulkarni, S. R.; Levitan, D. B.; Kasliwal, M. M.; Cenko, S. B.; Cao, Y.; Bellm, E.; Laher, R. R.
We have commenced a multi-year program, the Caltech-NRAO Stripe 82 Survey (CNSS), to search for radio transients with the Jansky VLA in the SDSS Stripe 82 region. The CNSS will deliver five epochs over the entire ∼270 deg^2 of Stripe 82, an eventual deep combined map with a rms noise of ∼40 μJy and catalogs at a frequency of 3 GHz, and having a spatial resolution of 3". This first paper presents the results from an initial pilot survey of a 50 deg^2 region of Stripe 82, involving four epochs spanning logarithmic timescales between one week and 1.5 years, with...

13. Secure RAID Schemes for Distributed Storage - Huang, Wentao; Bruck, Jehoshua
We propose secure RAID, i.e., low-complexity schemes to store information in a distributed manner that is resilient to node failures and resistant to node eavesdropping. We generalize the concept of systematic encoding to secure RAID and show that systematic schemes have significant advantages in the efficiencies of encoding, decoding and random access. For the practical high rate regime, we construct three XOR-based systematic secure RAID schemes with optimal or almost optimal encoding and decoding complexities, from the EVENODD codes and B codes, which are array codes widely used in the RAID architecture. The schemes can tolerate up to two node failures...

14. Incorporating Surface Diffusion into a Cellular Automata Model of Ice Growth from Water Vapor - Libbrecht, Kenneth G.
We describe a numerical model of faceted crystal growth using a cellular automata method that incorporates admolecule diffusion on faceted surfaces in addition to bulk diffusion in the medium surrounding the crystal. The model was developed for investigating the diffusion-limited growth of ice crystals in air from water vapor, where the combination of bulk diffusion and strongly anisotropic molecular attachment kinetics yields complex faceted structures. We restricted the present model to cylindrically symmetric crystal growth with relatively simple growth morphologies, as this was sufficient for making quantitative comparisons between theoretical models and ice growth experiments. Overall this numerical model reproduces ice growth behavior with reasonable fidelity over a...

15. Advanced Post-Processing Techniques of Molecular Dynamics Simulations in Studying Strong Anharmonic Thermodynamics of Solids - Lan, Tian
While the vibrational thermodynamics of materials with small anharmonicity at low temperatures has been understood well based on the harmonic phonons approximation; at high temperatures, this understanding must accommodate how phonons interact with other phonons or with other excitations. We shall see that the phonon-phonon interactions give rise to interesting coupling problems, and essentially modify the equilibrium and non-equilibrium properties of materials, e.g., thermal expansion, thermodynamic stability, heat capacity, optical properties, thermal transport and other nonlinear properties ofmaterials. To date the anharmonic lattice dynamics is poorly understood despite its great importance, andmost studies on lattice dynamics still rely on the harmonic or quasiharmonicmodels. With recent developement of computational...

16. Fresnel transmission coefficients for thermal phonons at solid interfaces - Hua, Chengyun; Chen, Xiangwen; Ravichandran, Navaneetha K.; Minnich, Austin
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 a microscopic perspective, interfacial phonon transport is described by transmission and reflection coefficients, analogous to the well-known Fresnel coefficients for light. However, these coefficients have never been directly measured, and thermal transport processes at interfaces remain poorly understood despite considerable effort. Here, we report the first measurements of the Fresnel transmission coefficients for thermal phonons at a metal-semiconductor interface using ab-initio phonon transport modeling and a thermal characterization technique, time-domain thermore ectance. Our measurements show that interfaces...

17. Transit timing variations for planets near eccentricity-type mean motion resonances - Deck, Katherine M.; Agol, Eric
We present a derivation of the transit timing variations (TTVs) of a pair of planets near the j:j - 2 second order resonance on nearly circular and nearly coplanar orbits. We show that the TTVs of each planet are given by sinusoids with a frequency of jn_2 - (j - 2)n_1, where n_2 and n_1 are the mean motions of the outer and inner planets, respectively. The amplitude of the TTV depends on the mass of the perturbing planet, relative to the mass of the star, and on a function of the eccentricities and longitudes of pericenter of each planet. The phase of each sinusoid...

18. Explicit MDS Codes for Optimal Repair Bandwidth - Wang, Zhiying; Tamo, Itzhak; Bruck, Jehoshua
MDS codes are erasure-correcting codes that can correct the maximum number of erasures for a given number of redundancy or parity symbols. If an MDS code has r parities and no more than r erasures occur, then by transmitting all the remaining data in the code, the original information can be recovered. However, it was shown that in order to recover a single symbol erasure, only a fraction of 1/r of the information needs to be transmitted. This fraction is called the repair bandwidth (fraction). Explicit code constructions were given in previous works. If we view each symbol in the code as a vector or...

19. Amorphous and ordered states of concentrated hard spheres under oscillatory shear - Koumakis, Nick; Brady, John F.; Petekidis, George
Hard sphere colloidal particles are a basic model system for general research into phase behavior, ordering and out-equilibrium glass transitions. Experimentally it has been shown that oscillatory shearing of a monodisperse hard sphere glass, produces two different crystal orientations; a Face Centered Cubic (FCC) crystal with the close packed direction parallel to shear at high strains and an FCC crystal with the close packed direction perpendicular to shear at low strains. Here, using Brownian dynamics simulations of hard sphere particles, we have examined high volume fraction shear-induced crystals under oscillatory shear as well as the same volume fraction glass counterparts....

20. The force on a body in active matter - Yan, Wen; Brady, John F.
We present a general theory for determining the force (and torque) exerted on a boundary (or body) in active matter. The theory extends the description of passive Brownian colloids to self-propelled active particles and applies for all ratios of the thermal energy kBT to the swimmer's activity k_sT_s = ζU^2_0T_R/6, where ζ is the Stokes drag coefficient, U_0 is the swim speed and T_R is the reorientation time of the active particles. The theory has a natural microscopic length scale over which concentration and orientation distributions are confined near boundaries, but the microscopic length does not appear in the force. The swim pressure...

Página de resultados:
 

Busque un recurso