For organisations like Facebook, high quality software is important. However, the pace of change ... more For organisations like Facebook, high quality software is important. However, the pace of change and increasing complexity of modern code makes it difficult to produce error-free software. Available tools are often lacking in helping programmers develop more reliable and secure applications. Formal verification is a technique able to detect software errors statically, before a product is actually shipped. Although this aspect makes this technology very appealing in principle, in practice there have been many difficulties that have hindered the application of software verification in industrial environments. In particular, in an organisation like Facebook where the release cycle is fast compared to more traditional industries, the deployment of formal techniques is highly challenging. This paper describes our experience in integrating a verification tool based on static analysis into the software development cycle at Facebook.
We report the detection of a transiting super-Earth-sized planet (R= 1.39 ± 0.09R⊕) in a 1.4-day ... more We report the detection of a transiting super-Earth-sized planet (R= 1.39 ± 0.09R⊕) in a 1.4-day orbit around L 168-9 (TOI-134), a bright M1V dwarf (V= 11,K= 7.1) located at 25.15 ± 0.02 pc. The host star was observed in the first sector of the Transiting Exoplanet Survey Satellite (TESS) mission. For confirmation and planet mass measurement purposes, this was followed up with ground-based photometry, seeing-limited and high-resolution imaging, and precise radial velocity (PRV) observations using the HARPS andMagellan/PFS spectrographs. By combining the TESS data and PRV observations, we find the mass of L 168-9 b to be 4.60 ± 0.56M⊕and thus the bulk density to be 1.74−0.33+0.44times higher than that of the Earth. The orbital eccentricity is smaller than 0.21 (95% confidence). This planet is a level one candidate for the TESS mission’s scientific objective of measuring the masses of 50 small planets, and it is one of the most observationally accessible terrestrial planets for future...
Wide field surveys for transiting planets are well suited to searching diverse stellar population... more Wide field surveys for transiting planets are well suited to searching diverse stellar populations, enabling a better understanding of the link between the properties of planets and their parent stars. We report the discovery of HAT-P-69 b (TOI 625.01) and HAT-P-70 b (TOI 624.01), two new hot Jupiters around A stars from the HATNet survey which have also been observed by the Transiting Exoplanet Survey Satellite (TESS). HAT-P-69 b has a mass of 3.73 +0.61 −0.59 M Jup and a radius of 1.626 +0.032 −0.025 R Jup , and is in a prograde 4.79-day orbit around a star of mass 1.698 +0.025 −0.025 M and radius 1.854 +0.043 −0.022 R. HAT-P-70 b has a radius of 1.87 +0.15 −0.10 R Jup and a mass constraint of < 6.78 (3σ) M Jup , and is in a retrograde 2.74-day orbit around a star of mass 1.890 +0.010 −0.013 M and radius 1.858 +0.119 −0.091 R. We use the confirmation of these planets around relatively massive stars as an opportunity to explore the occurrence rate of hot Jupiters as a function of stellar mass. We define a sample of 47,126 mainsequence stars brighter than T mag = 10 that yields 31 giant planet candidates, including 18 confirmed planets, 3 candidates, and 10 false positives. We find a net hot Jupiter occurrence rate of 0.45 ± 0.10 % within this sample, consistent with the rate measured by Kepler for FGK stars. When divided into stellar mass bins, we find the occurrence rate to be 0.71 ± 0.31 % G stars, 0.43 ± 0.15 % for F stars, and 0.32 ± 0.12 % for A stars. Thus, at this point, we cannot discern any statistically significant trend in the occurrence of hot Jupiters with stellar mass.
Traditional validation of flight control systems is based primarily upon empirical testing. Empir... more Traditional validation of flight control systems is based primarily upon empirical testing. Empirical testing is sufficient for simple systems in which a.) the behavior is approximately linear and b.) humans are in-the-loop and responsible for off-nominal flight regimes. A different possible concept of operation is to use adaptive flight control systems with online learning neural networks (OLNNs) in combination with a human pilot for off-nominal flight behavior (such as when a plane has been damaged). Validating these systems is difficult because the controller is changing during the flight in a nonlinear way, and because the pilot and the control system have the potential to co-adapt in adverse ways-traditional empirical methods are unlikely to provide any guarantees in this case. Additionally, the time it takes to find unsafe regions within the flight envelope using empirical testing means that the time between adaptive controller design iterations is large. This paper describes a new concept for validating adaptive control systems using methods based on Bayesian statistics. This validation framework allows the analyst to build nonlinear models with modal behavior, and to have an uncertainty estimate for the difference between the behaviors of the model and system under test.
Validating models of airspace operations is a particu-lar challenge. These models are often aimed... more Validating models of airspace operations is a particu-lar challenge. These models are often aimed at finding and exploring safety violations, and aim to be accurate representations of real-world behavior. However, the rules governing the behavior are quite complex: non-linear physics, operational modes, human behavior, and stochastic environmental concerns all determine the re-sponses of the system. In order to quantify uncertainty in the model (and by extension, risk in the real world), one recently successful methodology has been to de-velop a response surface replacement for the original model, and to learn the behavior of the system from the response surface. In this paper, we present a study on aircraft runway approaches as modeled in Geor-gia Tech’s Work Models that Compute (WMC) simu-lation. We use a new learner, Genetic-Active Learning for Search-Based Software Engineering (GALE) to dis-cover the Pareto frontiers defined by cognitive struc-tures. These cognitive structures o...
Validating a concept of operation for a complex, safety-critical system (like the National Airspa... more Validating a concept of operation for a complex, safety-critical system (like the National Airspace Sys-tem) is challenging because of the high dimensionality of the controllable parameters and the infinite number of states of the system. In this paper, we use statistical modeling techniques to explore the behavior of a conflict detection and resolution algorithm designed for the terminal airspace. These techniques predict the robustness of the system simulation to both nominal and off-nominal behaviors within the overall airspace. They also can be used to evaluate the output of the simulation against recorded airspace data. Additionally, the techniques carry with them a mathematical value of the worth of each prediction–a statistical uncertainty for any robustness estimate. Uncertainty Quantification (UQ) is the process of quantitative characterization and ultimately a reduction of uncertainties in complex systems. UQ is important for understanding the influence of uncertainties on...
Phantomlike elastomer simulations do not always deform globally affinely in the way that classica... more Phantomlike elastomer simulations do not always deform globally affinely in the way that classical theory predicts. Assuming that each crosslink will deform affinely with its topological neighbors gives much better results, and creates a way to isolate crosslinks with unpredictable deformation properties. The correlation of non-affinities and network properties depends on the constitutive model and boundary condition used. We always find a correlation between local density of crosslinks and degree of non-affinity.
For organisations like Facebook, high quality software is important. However, the pace of change ... more For organisations like Facebook, high quality software is important. However, the pace of change and increasing complexity of modern code makes it difficult to produce error-free software. Available tools are often lacking in helping programmers develop more reliable and secure applications. Formal verification is a technique able to detect software errors statically, before a product is actually shipped. Although this aspect makes this technology very appealing in principle, in practice there have been many difficulties that have hindered the application of software verification in industrial environments. In particular, in an organisation like Facebook where the release cycle is fast compared to more traditional industries, the deployment of formal techniques is highly challenging. This paper describes our experience in integrating a verification tool based on static analysis into the software development cycle at Facebook.
We report the detection of a transiting super-Earth-sized planet (R= 1.39 ± 0.09R⊕) in a 1.4-day ... more We report the detection of a transiting super-Earth-sized planet (R= 1.39 ± 0.09R⊕) in a 1.4-day orbit around L 168-9 (TOI-134), a bright M1V dwarf (V= 11,K= 7.1) located at 25.15 ± 0.02 pc. The host star was observed in the first sector of the Transiting Exoplanet Survey Satellite (TESS) mission. For confirmation and planet mass measurement purposes, this was followed up with ground-based photometry, seeing-limited and high-resolution imaging, and precise radial velocity (PRV) observations using the HARPS andMagellan/PFS spectrographs. By combining the TESS data and PRV observations, we find the mass of L 168-9 b to be 4.60 ± 0.56M⊕and thus the bulk density to be 1.74−0.33+0.44times higher than that of the Earth. The orbital eccentricity is smaller than 0.21 (95% confidence). This planet is a level one candidate for the TESS mission’s scientific objective of measuring the masses of 50 small planets, and it is one of the most observationally accessible terrestrial planets for future...
Wide field surveys for transiting planets are well suited to searching diverse stellar population... more Wide field surveys for transiting planets are well suited to searching diverse stellar populations, enabling a better understanding of the link between the properties of planets and their parent stars. We report the discovery of HAT-P-69 b (TOI 625.01) and HAT-P-70 b (TOI 624.01), two new hot Jupiters around A stars from the HATNet survey which have also been observed by the Transiting Exoplanet Survey Satellite (TESS). HAT-P-69 b has a mass of 3.73 +0.61 −0.59 M Jup and a radius of 1.626 +0.032 −0.025 R Jup , and is in a prograde 4.79-day orbit around a star of mass 1.698 +0.025 −0.025 M and radius 1.854 +0.043 −0.022 R. HAT-P-70 b has a radius of 1.87 +0.15 −0.10 R Jup and a mass constraint of < 6.78 (3σ) M Jup , and is in a retrograde 2.74-day orbit around a star of mass 1.890 +0.010 −0.013 M and radius 1.858 +0.119 −0.091 R. We use the confirmation of these planets around relatively massive stars as an opportunity to explore the occurrence rate of hot Jupiters as a function of stellar mass. We define a sample of 47,126 mainsequence stars brighter than T mag = 10 that yields 31 giant planet candidates, including 18 confirmed planets, 3 candidates, and 10 false positives. We find a net hot Jupiter occurrence rate of 0.45 ± 0.10 % within this sample, consistent with the rate measured by Kepler for FGK stars. When divided into stellar mass bins, we find the occurrence rate to be 0.71 ± 0.31 % G stars, 0.43 ± 0.15 % for F stars, and 0.32 ± 0.12 % for A stars. Thus, at this point, we cannot discern any statistically significant trend in the occurrence of hot Jupiters with stellar mass.
Traditional validation of flight control systems is based primarily upon empirical testing. Empir... more Traditional validation of flight control systems is based primarily upon empirical testing. Empirical testing is sufficient for simple systems in which a.) the behavior is approximately linear and b.) humans are in-the-loop and responsible for off-nominal flight regimes. A different possible concept of operation is to use adaptive flight control systems with online learning neural networks (OLNNs) in combination with a human pilot for off-nominal flight behavior (such as when a plane has been damaged). Validating these systems is difficult because the controller is changing during the flight in a nonlinear way, and because the pilot and the control system have the potential to co-adapt in adverse ways-traditional empirical methods are unlikely to provide any guarantees in this case. Additionally, the time it takes to find unsafe regions within the flight envelope using empirical testing means that the time between adaptive controller design iterations is large. This paper describes a new concept for validating adaptive control systems using methods based on Bayesian statistics. This validation framework allows the analyst to build nonlinear models with modal behavior, and to have an uncertainty estimate for the difference between the behaviors of the model and system under test.
Validating models of airspace operations is a particu-lar challenge. These models are often aimed... more Validating models of airspace operations is a particu-lar challenge. These models are often aimed at finding and exploring safety violations, and aim to be accurate representations of real-world behavior. However, the rules governing the behavior are quite complex: non-linear physics, operational modes, human behavior, and stochastic environmental concerns all determine the re-sponses of the system. In order to quantify uncertainty in the model (and by extension, risk in the real world), one recently successful methodology has been to de-velop a response surface replacement for the original model, and to learn the behavior of the system from the response surface. In this paper, we present a study on aircraft runway approaches as modeled in Geor-gia Tech’s Work Models that Compute (WMC) simu-lation. We use a new learner, Genetic-Active Learning for Search-Based Software Engineering (GALE) to dis-cover the Pareto frontiers defined by cognitive struc-tures. These cognitive structures o...
Validating a concept of operation for a complex, safety-critical system (like the National Airspa... more Validating a concept of operation for a complex, safety-critical system (like the National Airspace Sys-tem) is challenging because of the high dimensionality of the controllable parameters and the infinite number of states of the system. In this paper, we use statistical modeling techniques to explore the behavior of a conflict detection and resolution algorithm designed for the terminal airspace. These techniques predict the robustness of the system simulation to both nominal and off-nominal behaviors within the overall airspace. They also can be used to evaluate the output of the simulation against recorded airspace data. Additionally, the techniques carry with them a mathematical value of the worth of each prediction–a statistical uncertainty for any robustness estimate. Uncertainty Quantification (UQ) is the process of quantitative characterization and ultimately a reduction of uncertainties in complex systems. UQ is important for understanding the influence of uncertainties on...
Phantomlike elastomer simulations do not always deform globally affinely in the way that classica... more Phantomlike elastomer simulations do not always deform globally affinely in the way that classical theory predicts. Assuming that each crosslink will deform affinely with its topological neighbors gives much better results, and creates a way to isolate crosslinks with unpredictable deformation properties. The correlation of non-affinities and network properties depends on the constitutive model and boundary condition used. We always find a correlation between local density of crosslinks and degree of non-affinity.
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Papers by Misty Davies