Recursos de colección
Caltech Authors (129.911 recursos)
Repository of works by Caltech published authors.
Type = Report or Paper
Repository of works by Caltech published authors.
Type = Report or Paper
Masci, Frank J.; Laher, Russ; Rebbapragada, Umaa; Doran, Gary; Miller, Adam; Bell, Eric; Kasliwal, Mansi M.; Ofek, Eran; Surace, Jason; Shupe, David; Grillmair, Carl J.; Jackson, Ed; Barlow, Tom A.; Yan, Lin; Cao, Yi; Cenko, S. Bradley; Storrie-Lombardi, Lisa; Helou, George; Prince, Thomas A.; Kulkarni, Shrinivas R.
We describe the near real-time transient-source discovery engine for the
intermediate Palomar Transient Factory (iPTF), currently in operations at the
Infrared Processing and Analysis Center (IPAC), Caltech. We coin this system
the IPAC/iPTF Discovery Engine (or IDE). We review the algorithms used for
PSF-matching, image subtraction, detection, photometry, and machine-learned
(ML) vetting of extracted transient candidates. We also review the performance
of our ML classifier. For a limiting signal-to-noise ratio of 4 in relatively
unconfused regions, "bogus" candidates from processing artifacts and imperfect
image subtractions outnumber real transients by ~ 10:1. This can be
considerably higher for image data with inaccurate astrometric and/or
PSF-matching solutions. Despite this occasionally high contamination...
Cheung, Clifford; Remmen, Grant N.
We study the Gauss-Bonnet (GB) term as the leading higher-curvature
correction to pure Einstein gravity. Assuming a tree-level ultraviolet
completion free of ghosts or tachyons, we prove that the GB term has a
nonnegative coefficient in dimensions greater than four. Our result follows
from unitarity of the spectral representation for a general ultraviolet
completion of the GB term.
Ciosmak, Paweł; Hadasz, Leszek; Manabe, Masahide; Sułkowski, Piotr
In modern mathematical and theoretical physics various generalizations, in
particular supersymmetric or quantum, of Riemann surfaces and complex algebraic
curves play a prominent role. We show that such supersymmetric and quantum
generalizations can be combined together, and construct supersymmetric quantum
curves, or super-quantum curves for short. Our analysis is conducted in the
formalism of super-eigenvalue models: we introduce $\beta$-deformed version of
those models, and derive differential equations for associated
$\alpha/\beta$-deformed super-matrix integrals. We show that for a given model
there exists an infinite number of such differential equations, which we
identify as super-quantum curves, and which are in one-to-one correspondence
with, and have the structure of, super-Virasoro singular vectors. We...
Andersen, Jørgen Ellegaard; Gukov, Sergei; Pei, Du
We propose and prove the Verlinde formula for the quantization of the Higgs
bundle moduli spaces and stacks for any simple and simply-connected group. This
generalizes the equivariant Verlinde formula for the case of SU(n) proposed
previously by the second and third author. We further establish a Verlinde
formula for the quantization of parabolic Higgs bundle moduli spaces and
stacks.
Ursini, F.; Petrucci, P.-O.; Matt, G.; Bianchi, S.; Cappi, M.; De Marco, B.; De Rosa, A.; Malzac, J.; Marinucci, A.; Ponti, G.; Tortosa, A.
We present results from a joint Xmm-Newton/NuSTAR monitoring of the Seyfert 1
NGC 4593, consisting of 5x20 ks simultaneous observations spaced by two days,
performed in January 2015. The source is variable, both in flux and spectral
shape, on time-scales down to a few ks and with a clear softer-when-brighter
behaviour. In agreement with past observations, we find the presence of a warm
absorber well described by a two-phase ionized outflow. The source exhibits a
cold, narrow and constant Fe K alpha line at 6.4 keV, and a broad component is
also detected. The broad-band (0.3-79 keV) spectrum is well described by a
primary power law with Gamma=1.6-1.8...
Strader, Jay; Li, Kwan-Lok; Chomiuk, Laura; Heinke, Craig O.; Udalski, Andrzej; Peacock, Mark; Shishkovsky, Laura; Tremou, Evangelia
We report the discovery of an eclipsing low-mass X-ray binary at the center
of the 3FGL error ellipse of the unassociated Fermi/Large Area Telescope
gamma-ray source 3FGL J0427.9-6704. Photometry from OGLE and the SMARTS 1.3-m
telescope and spectroscopy from the SOAR telescope have allowed us to classify
the system as an eclipsing low-mass X-ray binary (P = 8.8 hr) with a main
sequence donor and a neutron star accretor. Broad double-peaked H and He
emission lines suggest the ongoing presence of an accretion disk. Remarkably,
the system shows shows separate sets of absorption lines associated with the
accretion disk and the secondary, and we use their radial velocities...
Politzer, David
Rim and back geometry determine much of the behavior of sound inside the pot, whose effect on total, produced sound is subtle but discernible. The theory of sound inside a cylinder is reviewed and demonstrated. And previous work on the Helmholtz resonance and the interplay between the Helmholtz resonance and the lowest head mode is revisited using some improved techniques.
Wang, M.; Brady, J. F.
We thank IBS for their comments which question our
interpretation of the universal viscosity divergence near
the flow-arrest transition in constant stress and pressure
rheology of hard-sphere colloidal suspensions [2]. IBS
introduced two Péclet numbers: Pe_0 = ẏ_ɑ^2=d0 and Pe = ẏ_ɑ^2/d(φ), with ẏ the strain rate, ɑ the particle size, d0
the isolated single-particle diffusivity and d_0 the long-
time at-rest self-diffusivity, and considered three regimes:
(i) Pe_0 < Pe ≪ 1, (ii) Pe_0 ≪ 1 ≪ Pe, and (iii) 1 ≪ Pe_0 <
Pe.
Wald, Lisa A.; Given, Douglas D.; Jones, Lucile M.; Hutton, L. Katherine
The California Institute of Technology together with the Pasadena Office of the
U.S. Geological Survey operates a network of approximately 280 remote seismometers
in southern California. Signals from these sites are telemetered to the central processing
site at the Caltech Seismological Laboratory in Pasadena. These signals are continuously
monitored by computers that detect and record thousands of earthquakes each year. Phase
arrival times for these events are picked by human analysts and archived along with digital
seismograms. All data aquisition, processing and archiving is achieved using the CUSP
system. These data are used to compile the Southern California Catalog of Earthquakes;
a list beginning in 1932 that currently...
Archibald, R. F.; Kaspi, V. M.; Tendulkar, S. P.; Scholz, P.
Radio pulsars are believed to have their emission powered by the loss of rotational kinetic energy. By contrast, magnetars show intense X-ray and gamma-ray radiation whose luminosity greatly exceeds that due to spin-down and is believed to be powered by intense internal magnetic fields. A basic prediction of this picture is that radio pulsars of high magnetic field should show magnetar-like emission. Here we report on a magnetar-like X-ray outburst from the radio pulsar PSR J1119-6127, heralded by two short bright X-ray bursts on 2016 July 27 and 28 (Kennea et al. 2016; Younes et al. 2016). Using Target-of-Opportunity data...
Quintero-Cadena, Porfirio; Sternberg, Paul W.
Enhancers physically interact with transcriptional promoters, looping over distances that can span multiple regulatory elements. Given that enhancer-promoter (EP) interactions generally occur via common protein complexes, it is unclear whether EP pairing is predominantly deterministic or proximity guided. Here we present cross-organismic evidence suggesting that most EP pairs are compatible, largely determined by physical proximity rather than specific interactions. By re-analyzing transcriptome datasets, we find that the transcription of gene neighbors is correlated over distances that scale with genome size. We experimentally show that non-specific EP interactions can explain such correlation, and that EP distance acts as a scaling factor...
Taghavi Larigani, Shervin; Heaton, Thomas H.
We have started to explore the feasibility of extracting useful data on the deformation of buildings and structures based on optical videos, (Taghavi Larigani & Heaton).
In the beginning, we look at the characterizations and limitations of the hardware, which is composed of a high-quality digital camera, combined with its optical imaging system capturing a video-footage of the structure under test, and then introduce a straightforward targets-tracking algorithm that produces the time-series displacements of targets that we select on the video.
We performed preliminary measurements consisting of testing our targets-tracking algorithm using high definition format videos displaying the structures that...
Nishizawa, Atsushi; Chen, Yanbei
In quantum physics, measurement error and disturbance were first naively thought to be simply constrained by the Heisenberg uncertainty relation. Later, more rigorous analysis showed that the error and disturbance satisfy more subtle inequalities. Several versions of universally valid error-disturbance relations (EDR) have already been obtained and experimentally verified in the regimes where naive applications of the Heisenberg uncertainty relation failed. However, these EDRs were formulated for discrete measurements. In this paper, we consider continuous measurement processes and obtain new EDR inequalities in the Fourier space: in terms of the power spectra of the system and probe variables. By applying...
Landon-Cardinal, Olivier; Yoshida, Beni; Preskill, John; Poulin, David
A two-dimensional topologically ordered quantum memory is well protected against error if the energy gap is large compared to the temperature, but this protection does not improve as the system size increases. We review and critique some recent proposals for improving the memory time by introducing long-range interactions among anyons, noting that instability with respect to small local perturbations of the Hamiltonian is a generic problem for such proposals. We also discuss some broader issues regarding the prospects for scalable quantum memory in two-dimensional systems.
Hu, Renyu; Seager, Sara; Yung, Yuk L.
Warm Neptune- and sub-Neptune-sized exoplanets in orbits smaller than Mercury's are thought to have experienced extensive atmospheric evolution. Here we propose that a potential outcome of this atmospheric evolution is the formation of helium-dominated atmospheres. The hydrodynamic escape rates of Neptune- and sub-Neptune-sized exoplanets are comparable to the diffusion-limited escape rate of hydrogen, and therefore the escape is heavily affected by diffusive separation between hydrogen and helium. A helium atmosphere can thus be formed -- from a primordial hydrogen-helium atmosphere -- via atmospheric hydrodynamic escape from the planet. The helium atmosphere has very different abundances of major carbon and oxygen...
Benneke, Björn
The elemental compositions of hot Jupiters are informative relics of planet formation that can help us answer long-standing questions regarding the origin and formation of giant planets. Here, I present the main conclusions from a comprehensive atmospheric retrieval survey of eight hot Jupiters with detectable molecular absorption in their near-infrared transmission spectra. I analyze the eight transmission spectra using the newly-developed, self-consistent atmospheric retrieval framework, SCARLET. Unlike previous methods, SCARLET combines the physical and chemical consistency of complex atmospheric models with the statistical treatment of observational uncertainties known from atmospheric retrieval techniques. I find that all eight hot Jupiters consistently...
Vogel, Petr
Evaluation of the reactor v_e flux and spectrum is an essential ingredient of their application in the neutrino oscillation studies. Two anomalies, i.e. discrepancies between the observed and expected count rates, are widely discussed at the resent time. The total rate is ~ 6% lower than the expectation at all distances > 10 m from the reactor. And there is a shoulder (often referred to as "bump") at neutrino energies 5-7 MeV, not predicted in the calculated spectrum. I review the ways the flux and spectrum is evaluated and concentrate on the error budget. I argue that far reaching conclusions...
Porter, Frank C.
The CKM matrix, VV, relates the quark mass and flavor bases. In the standard model, VV is unitary 3×3, and specified by four arbitrary parameters, including a phase allowing for CPCP violation. We review the experimental determination of VV, including the four parameters in the standard model context. This is an active field; the precision of experimental measurements and theoretical inputs continues to improve. The consistency of the determination with the standard model unitarity is investigated. While there remain some issues the overall agreement with standard model unitarity is good.
Goza, Andres; Liska, Sebastian; Morley, Benjamin; Colonius, Tim
Many immersed boundary methods solve for surface stresses that impose the velocity boundary conditions on an immersed body. These surface stresses may contain spurious oscillations that make them ill-suited for representing the physical surface stresses on the body. Moreover, these inaccurate stresses often lead to unphysical oscillations in the history of integrated surface forces such as the coefficient of lift. While the errors in the surface stresses and forces do not necessarily affect the convergence of the velocity field, it is desirable, especially in fluid-structure interaction problems, to obtain smooth and convergent stress distributions on the surface. To this end,...
Wilson, Justin H.; Song, Justin C. W.; Refael, Gil
Out-of-equilibrium systems can host phenomena that transcend the usual restrictions of equilibrium systems. Here we unveil how out-of-equilibrium states, prepared via a quantum quench, can exhibit a non-zero Hall-type response that persists at long times, and even when the instantaneous Hamiltonian is time reversal symmetric; both these features starkly contrast with equilibrium Hall currents. Interestingly, the persistent Hall effect arises from processes beyond those captured by linear response, and is a signature of the novel dynamics in out-of-equilibrium systems. We propose quenches in two-band Dirac systems as natural venues to realize persistent Hall currents, which exist when either mirror or...