The Role of Multiplicity in Disk Evolution and Planet Formation

The past decade has seen a revolution in our understanding of protoplanetary disk evolution and planet formation in single star systems. However, the majority of solar-type stars form in binary systems, so the impact of binary companions on protoplanetary disks is an important element in our understanding of planet formation. We have compiled a combined multiplicity/disk census of Taurus-Auriga, plus a restricted sample of close binaries in other regions, in order to explore the role of multiplicity in disk evolution. Our results imply that the tidal influence of a close (<40 AU) binary companion significantly hastens the process of protoplanetary disk dispersal, as ~2/3 of all close binaries promptly disperse their disks within <1 Myr after formation. However, prompt disk dispersal only occurs for a small fraction of wide binaries and single stars, with ~80%-90% retaining their disks for at least ~2--3 Myr (but rarely for more than ~5 Myr). Our new constraints on the disk clearing timescale have significant implications for giant planet formation; most single stars have 3--5 Myr within which to form giant planets, whereas most close binary systems would have to form giant planets within <1 Myr. If core accretion is the primary mode for giant planet formation, then gas giants in close binaries should be rare. Conversely, since almost all single stars have a similar period of time within which to form gas giants, their relative rarity in RV surveys indicates either that the giant planet formation timescale is very well-matched to the disk dispersal timescale or that features beyond the disk lifetime set the likelihood of giant planet formation.Comment: Accepted to ApJ; 15 pages, 3 figures, 3 tables in emulateapj forma

Fundamental building blocks of nanoporous networks from ultra-small-angle x-ray scattering (USAXS) and small-angle x-ray scattering (SAXS) experiments

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Title from PDF of title page (University of Missouri--Columbia, viewed on October 27, 2011).Thesis advisor: Dr. Peter Pfeifer.Vita.Ph. D. University of Missouri--Columbia 2010.A new method of structural analysis that measures the nominal dimensions of pores using ultra-small-angle x-ray scattering (USAXS) and small-angle x-ray scattering (SAXS) data is presented. The characterization technique developed is applied to highly porous carbons that are used for reversible methane and hydrogen storage based on physisorption. Data is analyzed and fit under the primary working assumption that there is only one size and shape of pore and that the number of pores present in the sample is accounted for by the sample porosity, [phi]. The procedure presented in this study is not restricted to the analysis of carbonaceous materials. It is applicable to any porous material in which the nanopore is the fundamental building block. The advantage of our technique in comparison to methods currently used to measure the size and shape of nanopores, is that in addition to a width, at least one additional characteristic length is determinedIncludes bibliographical reference

Artificial intelligence - finite element method - hybrids for efficient nonlinear analysis of concrete structures

Realistic structural analyses and optimisations using the non-linear finite element method are possible today yet suffer from being very time-consuming, particularly in case of reinforced concrete plates and shells. Hence such investigations are currently dismissed in the vast majority of cases in practice. The "Artificial Intelligence - Finite Element - Hybrids" project addresses the current unsatisfactory situation with an approach that combines non-linear finite element models for reinforced concrete shells with scientific machine learning algorithms to create hybrid AI-FEM models. The AI-based surrogate material model provides the material stiffness as well as the stress tensor for given concrete design parameters and the strain tensor. This paper reports on the current status of the project and findings of the calibration of the AI-based reinforced concrete material model. We successfully calibrated and evaluated k-nearest-neighbour, LGBM and ResNet algorithms and report their predictive capabilities. Finally, some light is shed on the future work of integrating the AI surrogate material models back into the finite element method in the course of the numerical analysis of reinforced concrete structures

Study of localization in the quantum sawtooth map emulated on a quantum information processor

Quantum computers will be unique tools for understanding complex quantum systems. We report an experimental implementation of a sensitive, quantum coherence-dependent localization phenomenon on a quantum information processor (QIP). The localization effect was studied by emulating the dynamics of the quantum sawtooth map in the perturbative regime on a three-qubit QIP. Our results show that the width of the probability distribution in momentum space remained essentially unchanged with successive iterations of the sawtooth map, a result that is consistent with localization. The height of the peak relative to the baseline of the probability distribution did change, a result that is consistent with our QIP being an ensemble of quantum systems with a distribution of errors over the ensemble. We further show that the previously measured distributions of control errors correctly account for the observed changes in the probability distribution.Comment: 20 pages, 9 figure

The frequency of binary star interlopers amongst transitional discs

Using Non-Redundant Mask interferometry (NRM), we searched for binary companions to objects previously classified as transitional discs (TD). These objects are thought to be an evolutionary stage between an optically thick disc and optically thin disc. We investigate the presence of a stellar companion as a possible mechanism of material depletion in the inner region of these discs, which would rule out an ongoing planetary formation process in distances comparable to the binary separation. For our detection limits, we implement a new method of completeness correction using a combination of randomly sampled binary orbits and Bayesian inference. The selected sample of 24 TDs belongs to the nearby and young star-forming regions: Ophiuchus (˜130 pc), Taurus-Auriga (˜140 pc) and IC348 (˜220 pc). These regions are suitable to resolve faint stellar companions with moderate to high confidence levels at distances as low as 2 au from the central star. With a total of 31 objects, including 11 known TDs and circumbinary discs from the literature, we have found that a fraction of 0.38 ± 0.09 of the SEDs of these objects are likely due to the tidal interaction between a close binary and its disc, while the remaining SEDs are likely the result of other internal processes such as photoevaporation, grain growth, planet-disc interactions. In addition, we detected four companions orbiting outside the area of the truncation radii and propose that the IR excesses of these systems are due to a disc orbiting a secondary companion

Stringy NJL and Gross-Neveu models at finite density and temperature

Nonlocal stringy versions of the Nambu-Jona-Lasinio and Gross-Neveu models arise in a certain limit of holographic QCD. We analyze the phase structure at finite density and temperature at strong coupling in terms of probe branes in the gravity dual. Comparison with the phase structure of the local field theory models shows qualitative agreement with some aspects, and disagreement with others. Finally, we explain how to construct the Landau potentials for these models by taking the probe branes off-shell.Comment: 32 pages, uses JHEP3.cls; v2, references added, version to be submitted to JHE

Pairing in fermionic systems: A quantum information perspective

The notion of "paired" fermions is central to important condensed matter phenomena such as superconductivity and superfluidity. While the concept is widely used and its physical meaning is clear there exists no systematic and mathematical theory of pairing which would allow to unambiguously characterize and systematically detect paired states. We propose a definition of pairing and develop methods for its detection and quantification applicable to current experimental setups. Pairing is shown to be a quantum correlation different from entanglement, giving further understanding in the structure of highly correlated quantum systems. In addition, we will show the resource character of paired states for precision metrology, proving that the BCS states allow phase measurements at the Heisenberg limit.Comment: 23 pages, 4 figure

Kepler-445, Kepler-446 And The Occurrence Of Compact Multiples Orbiting Mid-M Dwarf Stars

We confirm and characterize the exoplanetary systems Kepler-445 and Kepler-446: two mid-M dwarf stars, each with multiple, small, short-period transiting planets. Kepler-445 is a metal-rich ([ Fe/H] = + 0.25 0.10) M4 dwarf with three transiting planets, and Kepler-446 is a metal-poor ([ Fe/H] = -0.30 0.10) M4 dwarf also with three transiting planets. Kepler-445c is similar toGJ 1214b: both in planetary radius and the properties of the host star. The Kepler-446 system is similar to the Kepler-42 system: both are metal-poor with large galactic space velocities and three short-period, likely rocky transiting planets that were initially assigned erroneously large planet-to-star radius ratios. We independently determined stellar parameters from spectroscopy and searched for and fitted the transit light curves for the planets, imposing a strict prior on stellar density in order to remove correlations between the fitted impact parameter and planet-to-star radius ratio for short-duration transits. Combining Kepler-445, Kepler-446, and Kepler-42, and isolating all mid-M dwarf stars observed by Kepler with the precision necessary to detect similar systems, we calculate that 21+ 7 -5 % of mid-M dwarf stars host compact multiples ( multiple planets with periods of less than 10 days) for a wide range of metallicities. We suggest that the inferred planet masses for these systems support highly efficient accretion of protoplanetary disk metals by mid-M dwarf protoplanets.NSF DGE1144152, AST-1005313NASA NAS5-26555NASA Office of Space Science NNX13AC07GAstronom

Herschel/PACS View Of Disks Around Low-Mass Stars And Brown Dwarfs In The TW Hydrae Association

We conducted Herschel/PACS observations of five very low-mass stars or brown dwarfs located in the TW Hya association with the goal of characterizing the properties of disks in the low stellar mass regime. We detected all five targets at 70 mu m and 100 mu m and three targets at 160 mu m. Our observations, combined with previous photometry from 2MASS, WISE, and SCUBA-2, enabled us to construct spectral energy distributions (SEDs) with extended wavelength coverage. Using sophisticated radiative transfer models, we analyzed the observed SEDs of the five detected objects with a hybrid fitting strategy that combines the model grids and the simulated annealing algorithm and evaluated the constraints on the disk properties via the Bayesian inference method. The modeling suggests that disks around low-mass stars and brown dwarfs are generally flatter than their higher mass counterparts, but the range of disk mass extends to well below the value found in T Tauri stars, and the disk scale heights are comparable in both groups. The inferred disk properties (i.e., disk mass, flaring, and scale height) in the low stellar mass regime are consistent with previous findings from large samples of brown dwarfs and very low-mass stars. We discuss the dependence of disk properties on their host stellar parameters and find a significant correlation between the Herschel far-IR fluxes and the stellar effective temperatures, probably indicating that the scaling between the stellar and disk masses (i.e., M-disk proportional to M-star) observed mainly in low-mass stars may extend down to the brown dwarf regime.Natural Science Foundation of Jiangsu Province of China BK20141046Youth Qianren Program of the National Science Foundation of ChinaNational Aeronautics and Space AdministrationStrategic Priority Research Program >The Emergence of Cosmological Structures> of the Chinese Academy of Sciences XDB09000000Astronom