Repository of works by Caltech published authors.
Type = Report or Paper
Mostrando recursos 1 - 20 de 2.230
Improving Conical Scanning for Satellite Tracking On-The-Move - Karol, Robert; Ristroph, Gunnar
Mobile satellite antennas are gimbal-mounted with an active control system to keep the antenna pointed at the
target satellite. Short time-scale antenna stabilization is achieved with gyroscope feedback. Long time-scale
tracking of the satellite is maintained by scanning the antenna: The beam is intentionally nutated and the
resulting change in signal strength is used to estimate how well the antenna is aligned to the satellite. We review
the basic architectures for tracking with an outer control loop, assuming that the system is built upon a fast
inner stabilization loop. The problem is formulated in a generic mathematical way, not specific to RF satellite
communication. Approaches and...
Continuous Self Energy of Ions at the Dielectric Interface - Wang, Rui; Wang, Zhen-Gang
We present a simple, unified theory for the self-energy of an ion near a dielectric interface. Our theory accounts for both the short-range (solvation) and long-range (image force) electrostatic forces, charge polarization induced by these forces, and the cavity energy. In contrast to previous models, our self energy is continuous across the interface and thus applicable to both the water and air (oil) sides of the interface. With no fitting parameters, we predict the specific ion effect on the interfacial affinity of halogen anions at the water/air interface, and the strong adsorption of hydrophobic ions at the water/oil interface, in...
B and L at the SUSY Scale, Dark Matter and R-parity Violation - Arnold, Jonathan M.; Pérez, Pavel Fileviez; Fornal, Bartosz; Spinner, Sogee
We present a simple theory where baryon and lepton numbers are spontaneously broken at the supersymmetry scale. In this context R-parity must be spontaneously broken but the theory still contains a stable field which can play the role of the cold dark matter of the Universe. We discuss the spectrum of the theory, the properties of the dark matter candidate and the predictions for direct detection experiments. This theory provides a concrete example of exotic supersymmetric signatures associated with having the simultaneous presence of R-parity violating and missing energy signals at the Large Hadron Collider.
Spectroscopic Confirmation of the Rich z=1.80 Galaxy Cluster JKCS 041 Using the WFC3 Grism: Environmental Trends in the Ages and Structure of Quiescent Galaxies - Newman, Andrew B.; Ellis, Richard S.; Andreon, Stefano; Treu, Tommaso; Raichoor, Anand; Trinchieri, Ginevra
We present Hubble Space Telescope imaging and grism spectroscopy of the distant galaxy cluster JKCS041. Our survey yields 98 redshifts whose precision is typically ~20 times better than photometric estimates. We confirm that JKCS041 is a rich cluster and derive a redshift z=1.80 via the identification of 19 member galaxies, of which 15 are quiescent. These members are spatially aligned with diffuse X-ray emission seen by Chandra. As JKCS041 is the most distant known cluster with such a large and spectroscopically-confirmed quiescent population, it provides an unique opportunity to study the effect of the environment on galaxy properties at early...
The Rapid Decline in Metallicity of Damped Ly-α Systems at z∼5 - Rafelski, Marc; Neeleman, Marcel; Fumagalli, Michele; Wolfe, Arthur M.; Prochaska, J. Xavier
We present evidence that the cosmological mean metallicity of neutral atomic hydrogen gas shows a sudden decrease at z > 4.7 down to 〈Z〉 = -2.03^(+0.09)_(-0.11), which is 6σ deviant from that predicted by a linear fit to the data
at lower redshifts. This measurement is made possible by the chemical abundance measurements of 8 new damped Ly-α (DLA) systems at z > 4.7 observed with the Echellette Spectrograph and Imager on the Keck II telescope, doubling the number of measurements at z>4.7 to 16. The sudden decrease in metallicity is possibly due to the lower ultra-violet radiation field and higher...
A Near-Infrared Transmission Spectrum for the Warm Saturn HAT-P-12b - Line, Michael R.; Knutson, Heather; Deming, Drake; Wilkins, Ashlee; Desert, Jean-Michel
We present a HST WFC3 transmission spectrum for the transiting exoplanet HAT-P-12b. This warm (1000 K) sub-Saturn-mass planet has a smaller mass and a lower temperature than the hot-Jupiters that have been studied so far. We find that the planet's measured transmission spectrum lacks the expected water absorption feature for a hydrogen-dominated atmosphere, and is instead best-described by a model with high-altitude clouds. Using a frequentist hypothesis testing procedure, we can rule out a hydrogen-dominated cloud free atmosphere to 4.9σ. When combined with other recent WFC3 studies, our observations suggest that clouds may be common in exo-planetary atmospheres.
Constraints on Large-Scale Dark Acoustic Oscillations from Cosmology - Cyr-Racine, Francis-Yan; de Putter, Roland; Raccanelli, Alvise; Sigurdson, Kris
If all or a fraction of the dark matter (DM) were coupled to a bath of dark radiation (DR) in the early Universe we expect the combined DM-DR system to give rise to acoustic oscillations of the dark matter until it decouples from the DR. Much like the standard baryon acoustic oscillations, these dark acoustic oscillations (DAO) imprint a characteristic scale, the sound horizon of dark matter, on the matter power spectrum. We compute in detail how the microphysics of the DM-DR interaction affects the clustering of matter in the Universe and show that the DAO physics also gives rise...
Extracting Effective Higgs Couplings in the Golden Channel - Chen, Yi; Vega-Morales, Roberto
Kinematic distributions in Higgs decays to four charged leptons, the so called `golden channel, are a powerful probe of the tensor structure of its couplings to neutral electroweak gauge bosons. In this study we construct the first part of a comprehensive analysis framework designed to maximize the information contained in this channel in order to perform direct extraction of the various possible Higgs couplings. To that end we first complete an earlier analytic calculation of the leading order fully differential cross sections for the golden channel signal and background to include the 4e and 4μ final states with interference between...
Hadron production in e^+e^- annihilation at BABAR, and
implication for the muon anomalous magnetic moment - Porter, Frank C.
The BABAR collaboration has an extensive program of studying hadronic cross sections in low-energy e^+e^- collisions, accessible via initial-state radiation. Our measurements allow significant improvements in the precision of the predicted value of the muon anomalous magnetic moment. These improvements are necessary for illuminating the current 3.6 sigma difference between the predicted and the experimental values. We have published results on a number of processes with two to six hadrons in the final state. We report here the results of recent studies with final states that constitute the main contribution to the hadronic cross section in the energy region between...
Submm Recombination Lines in Dust-Obscured Starbursts and AGN - Scoville, N.; Murchikova, L.
We examine the use of submm recombination lines of H, He and He+ to probe the extreme ultraviolet (EUV) luminosity of starbursts (SB) and AGN. We find that the submm recombination lines of H, He and He+ are in fact extremely reliable and quantitative probes of the EUV continuum at 13.6 eV to above 54.6 eV. At submm wavelengths, the recombination lines originate from low energy levels (n = 20 - 50). The maser amplification, which poses significant problems for quantitative interpretation of the higher n, radio frequency recombination lines, is insignificant. Lastly, at submm wavelengths the dust extinction is...
Warm Spitzer and Palomar Near-IR Secondary Eclipse Photometry of Two Hot Jupiters: WASP-48b and HAT-P-23b - O’Rourke, Joseph G.; Knutson, Heather A.; Zhao, Ming; Fortney, Jonathan J.; Burrows, Adam; Agol, Eric; Deming, Drake; Désert, Jean-Michel; Howard, Andrew W.; Lewis, Nikole K.; Showman, Adam P.; Todorov, Kamen O.
We report secondary eclipse photometry of two hot Jupiters, WASP-48b and HAT-P-23b, at 3.6
and 4.5 μm taken with the InfraRed Array Camera aboard the Spitzer Space Telescope during the
warm Spitzer mission and in the H and KS bands with the Wide Field IR Camera at the Palomar
200-inch Hale Telescope. WASP-48b and HAT-P-23b are Jupiter-mass and twice Jupiter-mass objects
orbiting an old, slightly evolved F star and an early G dwarf star, respectively. In the H, KS, 3.6 μm,
and 4.5 μm bands, respectively, we measure secondary eclipse depths of 0.047% ± 0.016%, 0.109%
± 0.027%, 0.176% ± 0.013%, and 0.214% ± 0.020% for...
The next generation of µ → eγ and µ → 3e CLFV search experiments - Cheng, C.-h.; Echenard, B.; Hitlin, D. G.
We explore the possibilities for extending the sensitivity of current searches for
the charged lepton flavor violating decays µ → eγ and µ → eee. A future facility
such as Project X at Fermilab could provide a much more intense stopping µ^+ beam,
facilitating more sensitive searches, but improved detectors will be required as well.
Current searches are limited by accidental and physics backgrounds, as well as by the
total number of stopped muons. One of the limiting factors in current detectors for
µ → eγ searches is the photon energy resolution of the calorimeter. We present a new
fast Monte Carlo simulation of a conceptual design...
A Systematic Retrieval Analysis of Secondary Eclipse Spectra III: Diagnosing Chemical Disequilibrium in Planetary Atmospheres - Line, Michael R.; Yung, Yuk L.
Chemical disequilibrium has recently become a relevant topic in the study of the atmospheres of of transiting extrasolar planets, brown dwarfs, and directly imaged exoplanets. We present a new way of assessing whether or not a Jovian-like atmosphere is in chemical disequilibrium from observations of detectable or inferred gases such as H_2 O, CH_4, CO, and H _2. Our hypothesis, based on previous kinetic modeling studies, is that cooler atmospheres will show stronger signs of disequilibrium than hotter atmospheres. We verify this with chemistry-transport models and show that planets with temperatures less than ~ 1200 K are likely to show...
A Systematic Retrieval Analysis of Secondary Eclipse Spectra II: A Uniform Analysis of Eight Planets and Their C to O Ratios - Line, Michael R.; Knutson, Heather; Wolf, Aaron S.; Yung, Yuk L.
Secondary eclipse spectroscopy provides invaluable insights into the temperatures and compositions
of exoplanetary atmospheres. We carry out a systematic temperature and abundance retrieval analysis
of eight exoplanets (HD189733b, HD149026b, GJ436b, WASP-12b, WASP-19b, WASP-43b, TrES-2b,
and TrES-3b) observed in secondary eclipse using a combination of space- and ground-based facilities.
Our goal with this analysis is to provide a consistent set of temperatures and compositions from
which self-consistent models can be compared and to probe the underlying processes that shape these
atmospheres. This paper is the second in a three part series of papers exploring the retrievability of
temperatures and abundances from secondary eclipse spectra and the implications of...
Grid 2020: Towards a Policy of Renewable and Distributed Energy Resources - De Martini, Paul; Chandy, K. Mani; Fromer, N. A.
Caltech’s Resnick Sustainability Institute fosters transformational
advances in energy science and technology through research, education
and communication. Through its activities, the Institute strives to identify
and address the most important outstanding challenges and issues in the
generation, storage, transmission, conversion and conservation of energy.
To this end, the Institute provides leadership in brokering discussions on
energy and sustainability issues among panels of international experts in
government, academia, and industry. As part of its outreach, the Institute
issues summary reports documenting these compelling events.
The Resnick Institute is solely responsible for the content of this report. The
views expressed herein do not necessarily reflect the views of participants
in these discussions. This...
Particle Tracing: Revisited - Gharib, M.; Willert, C.
Particle tracing is a simple technique used to infer global quantitative
information regarding velocity and vorticity fields from
flow images. In this paper, recent advances in solving major
drawbacks associated with conventional particle tracing are discussed.
A quantitative automatic scheme which eliminates the
photographic step and is capable of constructing the velocity
field directly from the experimental set up is presented.
The Caltech-Jodrell Bank VLBI Surveys - Pearson, T. J.; Readhead, A. C. S.; Polatidis, A. G.; Wilkinson, P. N.; Xu, W.; Taylor, G. B.; Vermeulen, R. C.; Thakkar, D. D.; Henstock, D. R.; Browne, I. W. A.
Stochastic Analysis, Model and Reliability Updating of Complex Systems with Applications to Structural Dynamics - Cheung, Sai Hung
In many engineering applications, it is a formidable task to construct mathematical models
that are expected to produce accurate predictions of the behavior of a system of interest.
During the construction of such predictive models, errors due to imperfect modeling and
uncertainties due to incomplete information about the system and its environment (e.g.,
input or excitation) always exist and can be accounted for appropriately by using
probability logic. To assess the system performance subjected to dynamic excitations, a
stochastic system analysis considering all the uncertainties involved has to be performed. In
engineering, evaluating the robust failure probability (or its complement, robust reliability)
of the system is a very...
The smooth cyclotron line in Her X-1 as seen with NuSTAR - Fürst, Felix; Grefenstette, Brian W.; Staubert, Rüdiger; Tomsick, John A.; Bachetti, Matteo; Barret, Didier; Bellm, Eric C.; Boggs, Steven E.; Chenevez, Jerome; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Harrison, Fiona; Klochkov, Dmitry; Madsen, Kristin K.; Pottschmidt, Katja; Stern, Daniel; Walton, Dominic J.; Wilms, Jörn; Zhang, William
Her X-1, one of the brightest and best studied X-ray binaries, shows a cyclotron resonant scattering feature
(CRSF) near 37 keV. This makes it an ideal target for detailed study with the Nuclear Spectroscopic Telescope
Array (NuSTAR), taking advantage of its excellent hard X-ray spectral resolution. We observed Her X-1 three
times, coordinated with Suzaku, during one of the high flux intervals of its 35 d super-orbital period. This
paper focuses on the shape and evolution of the hard X-ray spectrum. The broad-band spectra can be fitted
with a powerlaw with a high-energy cutoff, an iron line, and a CRSF. We find that the CRSF...
Periodic and Aperiodic Variability in the Molecular Cloud ρ
Ophiuchus - Parks, J. Robert; Plavchan, Peter; White, Russel J.; Gee, Alan H.
Presented are the results of a near-IR photometric survey on 1678 stars in the direction of the ρ Ophiuchus (ρ Oph) star forming region using data from the 2MASS Calibration Database. For each target in this sample, up to 1584
individual J, H and K_s band photometric measurements with a cadence of ~ 1 day are obtained over 3 observing seasons spanning ~2.5 years; it is the most intensive survey of stars in this region to date. This survey identifies 101 variable stars with ΔK_s band amplitudes from 0.044 to 2.31 mag and Δ(J-K -s) color amplitudes ranging from 0.053 to...